Capacitor

Your post suggests these caps are on the output of your preamp, please confirm.  We need to know to output impedance of your preamp. Please share that. Also please share the input impedance of the amp you are using. With this info I can help you decide. 
I think the Milflex are good, but not great.  The VH Audio Odams sound better in every sonic way and are much smaller making for easier fit. 
Let us know. 

If your amp’s input impedance is really that high - 470k, then even a .22uf is fine! To assure it works with most any SS amp you may get in the future, then I would suggest any value from 1.5 uf - 2.2uf. It is best to keep the cap value as low as is reasonable as it helps sound quality. Bigger value caps, of the same brand, won’t sound quite as good as smaller values in that output position. Your preamp’s output impedance is not crazy high, but likely varies by frequency and volume. Depends on the circuit.
To assure no bass roll off with most any SS amp in the future, coupled with my comment on larger cap values, stick with 1.5 - 2.2 uf. I see no reason to use a higher value cap. I have built many tube preamps with output caps values of .47uf to 1.5uf with no issues at all feeding SS amps with input impedances of 47k and over. A 2.2uf value VH Audio Odam is my strong recommendation.  

With tube amps you are good with output caps from .47uf to 2.2uf.  If you want a more holographic image I suggest two cap brands.  
- VH Audio Odams 
- Duelund CAST CuSn - tinned copper version 

If cost is the issue, then consider a smaller value VH Audio Odam. Perhaps a 1.0 uf. In the end if these are still too costly for you, then a Miflex will be better than the others you mention. Yes, I have used all the caps you mentioned.

Please be aware that the Miflex caps are huge and may not fit easily based on the value you decide on. Check for fit first.  Simply look up the dimensions and make a mock up using a properly cut and rolled piece of paper or thin card stock. 

The Odams are much better than the Jantzen Superior Z which I am very familiar with. Different level of sonic performance and nuance to be frank. However, they do cost more.  Where are you located? 

If the caps are not on the output, but interstage, you should stick with the value they have.  I am only talking about the output cap position.  The caps tied to the the RCA outputs! 

Bpoletti, I am sorry but in this  case you could not be more incorrect.  Honestly. 
Pauly, no worries as the 3.3uf will sound great. Just wonderful. Order matched sets within 2% from the supplier.  Also, be sure to make note of the outer foil end and directionality of these caps. 

If by signal he means they are on the RCA outputs, then yes you can change. Don’t change the value of interstage coupling caps. 

If money is no problem and they fit….the Duelund CAST Cu(Sn).  This is the best sounding capacitor ever produced in my opinion.  

The Odams are far better! Nice job with the Cutf upgrade! Just wait till they break in fully! 

Pay attention to outer foil and direction. Enjoy.  That is a great combo! 

My go to cap for years.  Used literally dozens of them. Great sounding cap for sure. But, the VH Audio newer Odams are better sounding based on my experience.  More open, improved bass and dynamics. 

Vcap Odams are the better choice, vs Jupiter, as I use both in speaker and electronics applications.  Not close.  This is something I can say with 110% confidence. You will like the Jupiter, no doubt, but miss out on what the Odams do better. 

Odams are simply more real sounding than Jupiter copper foils. Improved realism. The stage is more open and speakers disappear more than Jupiter. Bass has more impact with the Odams. The Odams are more dynamic. Odams are more at ease and in perfect balance top to bottom at higher volumes.
Odams are a tad warm with great tonality. The Jupiters are better at fine inner details and are a tad more lively on top.

My favorite capacitor is the Duelund CAST tinned copper version.  They are available at HiFi Collective in the U.K.   They ship fast however.  Next is the Odam and then Jupiter copper foils. 

Well hello again. Yes sir, try Wima on your own folks and see they are flat sounding and mediocre at best. Others have reviewed the Wima and found the same. Best to learn for yourself fellow Agoners. They are not expensive to try.

Odams are great in speakers. Be aware of break in time as it is real with these Odams.  They take some 75-100 hours to fill in and open up.  A tad constipated sounding on first few hours.  After just 30 hours much better.  
They are directional so pay attention to outer foil. 

Yes, many use Wima as they are decent and inexpensive. It’s a cost issue and manufacturers must hit a cost and price point. Also a form issue. They are perfectly sized and proportioned for circuit boards. Also many high end manufacturers use VH Audio and Duelund in THE most important circuit positions such as output and coupling. These are builders in the know and open minded enough to actually try boutique caps!

Also, if we go by your reasoning why do the same companies using Wima caps also use many other middle of the road parts that simply meet spec. That’s it….meet spec on paper. These parts don’t offer SOTA sound quality. Look at all the gear built using sand cast resistors, Alps $20 pots and on and on….We are unfortunately talking about gear selling for many thousands! They use these parts for cost reasons and sometimes because they are not open to learning and experimenting with boutique parts. Designers are not necessarily skilled or expert in parts selection based on sound quality because they don’t have the time or inclination to dig into it.  That simple. This topic of part sound quality and personality is it’s own area of study with much to be learned. It takes time and effort. Even great designers like Nelson Pass say they are not interested in delving into it. He does not. Just not his interest or curiosity. This is common.

Let’s all just enjoy what we have found that works for our ears and music. No need to argue. I am happy for Raul.  He has found what works for him and that is great.  I tried Wima based on his experiences and did not like them. I did try them however in a crossover as I am always open to learning.  Enjoy Raul and my fellow DIYers.  Have fun!

Yes.  All good.  Agree with you.  The OP should hear all opinions. 

Yes Odams require at least 60 hours before even commenting on them 😊.   They will not go downhill after 60 hours and after 100 hours you are 85% there! 

They also sound flat and 2D which is an electronic artifact, not the sound intended on many good recordings. 

I would not use a bypass cap in a crossover. Don’t think they sound right in this application. Makes the sound sort of nervous. One great cap is better. Bypass caps are great in power supplies and SOMETIMES in coupling and output positions. It depends on the combo of caps used. 

Odam and Cutf sound wonderful together in electronics.  The .01uf Cutf combined with a .22-3 uf Odam works great.  You get a little more air and detail.  
I personally prefer the sound of Odam over the Cutf used alone. The Cutf is just too lively and exposing for  my tastes. This is a personal preference thing for me however. 

My post spelled that out if you go back and look at it. Bypassing does not always work well.  Trial and error at best. Some combos don’t sound quite right. I know Odam and Cutf work well in electronics.  I don’t like bypassing in crossovers as often times the result while impressive at first, more air and details, in the end can sound a tad nervous and not quite right.  Bypassing with film caps in power supplies with electrolytic caps is most always a nice plus.  

Yes indeed. Agreed. The Cutf .01uf and Odam do make magic together in electronics such as your Pre. I use the combo all the time in Orchid dac upgrades.  

👍

Patience is hard right now. I get it. The sound will go south at around 35-50 hours for a short time.  After this all gets better up to 200 hours or so. They will open up, smooth out and bass will fill in more at full burn in. Just the way it is with these tightly wound and damped foil caps.

I like Vcap Odam much more than Miflex . Just pulled out Miflex and replaced with Odam in my amp. Much better after break in. Everything improved from bass to highs.  More depth, more inner detail…..you get it. 
Miflex are forward sounding and not as smooth and detailed as Odams. Odams are even better sounding than Jupiter copper in my experience, but I shared this already. 

18 pieces! How can that be? Well yes that is quite some money. Please remind me of the amp model we are talking about here and the positions you are using them. I assume not as bypass caps in the power supply?  Thanks.
Bill

Yes, those are coupling caps and are certainly and important ingredient to your amplifier’s sound.
Those are wonderful amplifiers with great build quality. I owned the 339 monoblock Reference amps and enjoyed them tremendously. Canary used Hovland capacitors for years. Hovland only makes the black colored Supercaps now. Are they in your amp now? Perhaps the older blue or yellow colored Hovland caps? Please let me know. Please let me know what’s in there now and I can help you decide if an upgrade is worth it and which ones are worth the time, money and effort.

The Miflex are forward sounding. If you want a more immediate and forward sound, then they will do that. I found their presentation was impairing my ability to enjoy music over longer listening sessions, Just too forced and compared to being at ease and set back a tad further.

Those amps deserve the best and will reflect the sound quality upgrade the right part will deliver. If you have the black Hovland Supercap, then I would not replace with Miflex. Not a worthwhile investment in time, dollars and effort.

If the discounted price on the Odam caps is still too high, then I would stick with what you have. Other caps priced at $20-$30 each would be a sideways move for the most part. On paper, I would think the Miflex copper cap an upgrade, but my ears and experience have not proved that out.

Some of this is subjective for sure. That is why I asked if you want a more forward and upper mids highlighted sound. If you do, then the Milflex caps may be for you. Also, the cap must fit in the given space. The Miflex are huge!

The Theta caps are really not bad. Forget the Humble Audio Review site comments on these as in electronics they are pretty good really.
That said, your amps are top notch and upgrading to VH Audio Odams is something you will hear and appreciate post burn in. You won’t have to strain to hear how much better the amps will sound. If you buy 16 the cost is some $63 each. I would contact Chris of VH Audio and see if he would work with you on another 10-15% off? Never know. These will be better than the Jupiter copper. If you get the price closer to $50-$55 each, then the 16 will cost about $320 more for the entire amp upgrade. Money well spent if you want to hear the most from your amp and plan to keep it for a long time. 

Again, the HT’s will cost “about” the same as Odam? Why not go for the better Odam?! The HT’s are warm and full bodied sounding. Very musical. They are not on the level of the Odams however in most ways really. Not heard the Rike.

Yes, the HTs are better than the Theta. They will not give you the realism, inner detail, dynamics and bass articulation of the Odam. Jupiter has stopped making the HT as they are very time consuming to make. Limited inventory left on them.

The True Coppers are also better than the Theta. Just because they are film/paper and foil like the HT does not mean they will sound as good as the Odam. They won’t. You may have an aversion to the Odam’s based on something other than price? Seems that way anyway.

Don’t go by Humble Audio cap reviews solely as the caps were ONLY tested in a speaker crossover, not electronics. That is a very important distinction. Also, on a tweeter mostly! Caps can and do perform differently in high voltage electronic positions.

The Odams are not at all over detailed or bright or forward. No, they are richly detailed with natural warmth and fulsome bass foundation. They are the best of the ones you have mentioned. Frankly, I like them as much as the much more costly Duelund CAST in electronics. Yes, that good.

If you must stay within a given budget, then this would be a suggested order of performance hierarchy to consider. 
1) True Copper & Jupiter HT would be good choices.  True Copper will deliver slightly better resolution, inner detail and bass articulation.  The HT will be warmer, darker sounding, with rounder bass lines. 
2) Miflex will be like the True Copper, but more forward and lively in the upper mids and highs.