B&W 803D crossover caps

I am considering an upgrade of the crossover capacitors in by B&W 803Ds, particularly the mid and HF coupling caps.

I took out the top bass driver to find out what caps were installed. It looks like for the diamond tweeter B&W uses a Mundorf Supreme silver/gold, 4.7 mfd 1200V. For the mid driver there are two; a 47 mfd Mundorf MKP 400V series coupling cap (in series with the driver) and a 10 mfd Mundorf Supreme siver/gold bypassing cap (parallel to the driver).

I was thinking about changing out all three, but have a few concerns.

I was going to replace the 10 mfd, 4.7 mfd Supreme silver/gold with Supreme silver/gold/oil. Would there be enough of a difference in these two types to justify the cost? I also do not want to make the upper end any brighter.

I am also concerned about the long term reliability of oil filled caps, as some failures have been reported in warmer environments. I wonder if B&W did not use the silver/gold/oils for that reason.

The biggest impact I suspect will come from the replacement of that series 47 mfd MKP. I would probably use either the Mundorf MCap EVO (Al metalization), MCap EVO oil (Al/oil), or the MCap EVO silver/gold/oil. All three are the same size for 47 mfd, and will fit to replace the MKP. Barring the issues about oil, which might be the best sounding? Again, I want to avoid too much enhancement of the upper midrange.
I use the Jupiter copper caps and have never had an issue. You will never have an issue in a speaker crossover as there is no heat. Heat is the only factor of concern with these caps. I use them in tube amps with heat and still no problems. 

I have had them in my speakers and gear since they were introduced perhaps two years ago. So much better than any Mundorf caps based on my considerable cap rolling experience.  They are far more quiet, they remove noise better than the Duelund CAST. They are SOTA for micro details and exhibit a nice airy, natural tone. I prefer them to Duelund as they are more neutral through the upper mids. Very special cap. 
Over the last few days I have had a chance to complete the mods to my crossovers. Thanks to all for their suggestions.

I had to remove the upper bass driver and the mid range FTF driver to get at the crossovers and the wiring. I also removed the tweeter but I will get to that challenge below.

The XOs are mounted on plastic standoffs that are a bear to release the PC boards from. B&W slops glue on top of the barbs that hold the boards to the standoffs, and getting all the glue from the barbs usually means destroying the barbs. I contacted B&W and their CS was kind enough to send me back ups (they are not listed in their parts lists). I ended up pulling the two front standoffs and replacing them with a threaded insert designed for wood. My local hardware store had some that fit the .280" holes perfectly (use 5/16", for #8 screws). With .25" tall spacers, these mounted the boards perfectly.

The HF XO board is mounted on the roof of the midrange chamber, the MID XO is mounted on the floor. To remove the HF XO you have to release the board from the standoffs, then cut a number of tie wraps to release all the wiring. The HF XO is fed with two 12 ga wires (red/black) terminated in gold plated tab connectors (nice). Another pair of 12 ga black/red are soldered to this board and are terminated in a Molex connector that feeds the tweeter. I did find many of the tab connectors to be very loose, so I had to correct that before re-connecting.

I ended up swapping out the Supreme SG 4.7 mFd for an identically sized Supreme SGO. I also pulled the 0.5 OHM tab power resistor (no name on it) and replaced it with a 0.75 OHM 1% 100W MP9100 Caddock thick film resistor that mounted to the OEM heatsink perfectly. I used 0.75 OHM instead of the 0.5 OHM to reduce the tweeter output slightly. B&W originally spec'd a 1.0 OHM which they changed mid production to 0.5 OHM.

For the MID XO, I also swapped out the 2 OHM resistor with a 2.0 OHM 1% Caddock MP9100. I pulled the MKP 47 mFd Mundorf film cap and replaced it with an EVO SGO 47 mFd. This cap also fit quite nicely. I had PartsConnex match a couple to under 1%.

After re-mounting the XOs, I soldered all the gold plated tab connectors to the wire they were crimped to. Unusually, some were soldered by B&W and some were not. B&W also used some sort of grease on the connectors (not necessary for gold connectors IMHO) so I removed that as well. I pulled all three bass drivers to tighten and solder connections.

Now the tweeters. I strongly suggest most users leave these guys alone. They are extremely fragile and you must not touch that diamond diaphragm if at all possible. In mine, I felt a little too much front to back play, so I thought something might be loose. The motor unit/diaphragm is coupled to a bar that runs rearward through the end of the casing tube. At the end of this bar, a soft, gooey gasket material (looks like Sorbothane with the consistency of a gummy bear that has been on a hot sidewalk) surrounds the bar and isolates it from the casing. When you pull the motor and bar forward, you inevitably destroy this gasket as it sticks like crazy to the bar, and turns itself inside out as you pull forward. So order a backup from B&W before you disassemble the guts of the tweeter.

In my tweeter, the plastic coupling nut that holds the bar to the motor was loose. And you cannot tighten this nut unless you pull the guts of the tweeter out.

After all was put back together, I had a chance for some preliminary listening. I have to say the total end result was more pleasing than I anticipated. If I have to use a single word, it would be "smooth". Edginess on horns and vocal sibilants was gone. Bells and symbols are now slightly recessed in volume, but still very clear in position, with more 3d space between them. The overall sound fill left to right is vastly improved, with sound spilling outside the boundary of the left and right speakers (something I have been struggling to get with these 803d's for some time). The midrange seems to be separated better from the bottom end in clarity (this is hard to describe), so the bass transients no longer "mask" some of the midrange, as they had done before.

All in all, I am very happy with the changes.
Um, why not go to active crossovers and get the most control of the drivers and how they sound?  A lot easier than the "black arts" of trial and error using different caps.

Because that route is fraught with just as many variables and complexities. I was going to do that with another previous set of speakers and ended up buying the B&Ws instead.

To do what you suggest  first you need 3 to six power amps, depending on if you use stereo or mono amps. You need to adjust the output levels of each amp with each driver, so you need an RTA/pink noise setup to do it right. Then you need a decent XO setup. Anyone know of discrete component class A XOs that have three XO points? And a choice of first, second, or third order slopes? No? Me neither.  There are XOs out there, but most are op-amp based which is unacceptable to me. Finally, if you are using B&W drivers, you have to have impedance and parameter data for the drivers which is unobtanium unless you measure it yourself.

As I stated I considered building my own speakers prior to buying the B&Ws, and was going to go the full active route. But I could never get over the compromises and costs, plus I cannot design a cabinet like B&W does. 

Thank you for sharing your crossover upgrade experiences - I previously owned the 803D and 803 Diamond speakers - great value high tech speakers with timeless industrial design.