EL34 tubes- alternates to matched octet for Primaluna HP dialogue premium

I have the Primaluna Dialogue Premium HP power amp that uses 8 EL34 tubes.  I am currently using the stock EL34s, but have noticed a nice improvement in imaging when I switched to NOS mullards 12au7s.

As I look at playing around with different power tubes, (especially NOS Varieties) I see numerous sets of matched quads out there, but never matched octets, unless they are new production.

my question is this:  what do I lose sonically by using unmatched tubes, or two sets of matched quads, or four sets of matched pairs?  Wondering if since the Primaluna is self biasing, if it is less sensitive to non-matched tubes than other amps? 

So long as you are using the same brand/type you won’t lose much, if anything, due to the auto bias circuit in the PL amp. FWIW you have much to gain by considering different small NOS tubes, but not so much, I think, when considering power tubes which are usually verrry expensive and often not much better, if any, than some of the new production tubes currently available. Personally I would try new production tubes before going to NOS power tubes. In my Dialogue One I enjoy either JJ E34L’s or SED 6L6CG’s, the former warmer but having nice, clear highs, the latter a much more linear tone.
I have an HP as well and have used those NOS Mullards (the 8136 variety?) on my front end as well. Huge difference. Worth the $$ IMO and we are talking $120 per tube.

Theoretically, you can put 8 different EL34s in there and due to the PL self-biasing, it should work fine. but even Upscale Audio (kevin deal part owner of PrimaLuna) doesn't recommend this at all. I dont know the specifics, but makes sense on a  common sense level.

@newbee makes a good point about trying modern production tubes  before the greater expense of a full Octet of NOS tubes. But sometimes I want to take my upgrade climb 2 levels, not just one. The new production tubes get you 1 level. NOS gets you 2-3 levels higher. 

To save some money and intermediary steps, consider going straight to NOS if you will be using that amp for years to come. If you get the 8 modern tubes, listen for a month, then desire to go up to the next level, then you've got 8 tubes on your hands to have to sell. 

IMO< any upgrades to the PL HP integrated helps the whole system. It think of it as a great foundation/blueprint to build on with tubes specific to your system and room. 
If I had your integrated I probably would be tempted to try the kt150s just based on all the favorable reviews. They will not work in my El34 amp. I have used old stock mullards and a few new production tubes. But the best has been the Gold Lion kt77s I purchased from Upscale Audio.
There are several references to the PL integrated.  I have the power amp version, running a separate preamp.  I assume the comments apply to the power amp version as well as the integrated.

to 1graber2- yes the 8136 mullards at 120 each.  Might be the best money I have ever spent for a sonic improvement, best bang for the buck.
Get you two matched quads of Shuguang 6CA7-Z 50 Year Treasure Tubes (Black Bottle) and just kick back and enjoy the music, have had great luck buying these from a couple different venders on Ebay, just remember to get their premium grade.
Matched modern power tubes are fine.  8 matched NOS power tubes would cost way too much, and besides, you won’t really find 8 matched tubes- there aren’t enough of them to sort and match them like they can new production.  The recommendation for 8 premium matched Shuguang Treasure tubes is a viable answer to your question, but is almost absurd; too expensive to put so many in a budget amp.   
   The small signal tubes make the most difference and the cost is justifiable (to an audiophile, hah!)
   If you must, Mesa can sell you a set of matched Siemens EL 34’s.
@lloydc - you must have never been to Upscale Audio store or website. They have plenty of matched NOS tubes. I just bought 8 NOS Mullard CV4003 12AU7 and will order 12 new high grade Brimar’s for my amps. I definitely stay away from eBay sellers for tubes and go to UA. 

@meiatflask - I would definitely reach out to Kevin Deal and team for advice on the sound improvements you’re seeking. I have KT150 in my PL HP monoblock amps and they sound incredible.

Blues41, Small signal tubes are plentiful and to some degree afordable.  I was referring to power tubes. 8 old matched Mullard el34’s?  You can’t be serious.
@lloydc sorry I misread power tubes. I was speaking in terms of NOS 12au7’s. 

bluesy41- in what way are the KT150 better than the stock EL34?  midrange warmth, imaging, detail, soundstage, bass?   are they a "blow me away" change? and who's KT150s are you using?

tooblue & lloydc- are the Shuguang 6CA7-Z 50 Year Treasure Tubes a "nice improvement" over the stock EL34s or a "blow me away" change?

the NOS mullards 12au7 was a blow me away change in terms of soundstage and imaging.  I am wondering if I can find a similar improvement in the power tubes.  And I am not opposed to spending a few bucks.  After all, the other option to serious upgrade is a better amp, which is a whole lot more money than tubes.
I had that exact amp for a while and had a lot of fun doing some shootouts with various EL-34s and KT-120s.  The clear standouts were the NOS RFT EL-34s and the PSVane EL-34s.  I could have lived happily with either set and they made a huge difference over the stock tubes.  Huge.  Particularly in the highs (less harsh than the stock tubes—but my system is very resolving and accentuates sharp highs when they are present), and much warmer miss and overall fuller richer sound.  

I didn’t have the guts (money) to spring for anything like NOS Mullards or Siemens.  Those are crazy expensive.  RFT manufactures EL-34s for Siemens and others back in the day so I think it’s a good way to try something that should be in the same league for a lot less money and see what you think.  A matched quad of those is $250 or less on eBay.   I stuck with those and never looked back.  Until I switched amps of course (that was 3 amps ago).  The journey never ends.  Enjoy yours.  
@meiatflask - I have Magnepan 20.7 Planar speakers and so my amps came with stock EL 34 which were very warm and gave me that very intimate tube sound that we all love, but lacked in the area of bass and dynamics compared to the KT150’s. I also believe the 150’s expands the soundstage a few rows further than the EL34’s. More like being in the 5th row. You do lose some of the subtle nuances and inner detail that the EL34’s give but I’m talking a fraction. I have the Tung-Sol KT150’s and IMHO they are simply bad-ass.

@meiatflask, I have a set of 8 Premium Grade Black Bottle Treasure tubes with about 600 hours on them so they are broken in, pulled them from my VTL MB125s that are boxed up to go back to factory for rebuild, if you pay the shipping to you and back to me, you are welcome to try them out for a month or so. Let me know.
@tooblue - sounds like an offer I can’t refuse.  How do we do this? Can you send me a message/email outside of the discussion so we can word out the details directly?
I experienced reliability issues with Psvanne  Ax7’s.  Wish it were not so, they sounded nice.
@lloydc , FWIW I currently run 10 of Psvane 12A tubes in 6 different pieces with 1,000s of hours with no issues, looking for a piece of wood to knock on, and have had them in the past as well as running the treasure power tubes in my amps, give them a second chance especially if you liked them and make sure they are premium grade.

NOS preamp tubes are often affordable and I like 'em, but with power tubes I prefer the new stuff. I've used new Gold Lion KT88s and various Tung Sols including KT120s and 150s,  and they all work well, sound great,  and came with warranties.