I just went down this same road with a set of 804s. I found that on complicated musical passages or moderate volume the sound of the speakers would get harsh and muddled. I talked to B&W and they said that what I was hearing was lack of amplifier power. They recommended at least 250W per channel. So I started down the road to find the right amplifier.
I tried a lot of amps and was lucky to be able find a lot of places to demo amps with my same speakers, and a few places that let me do in home audtions. In my first go around the only pre-amp and amp combo that I found to work really well and eliminate the above issues was the A308 combo from Musical Fidelity. It sounded unhurried and very good, maybe even a touch polite.
About this same time, I had just upgraded to an HDTV and had bought a Denon 3910 for video. Turns out it is very good stock for Redbook CD play, in fact as good as my Millenium DACII. It was made by Ric Schultz and I discussed mdding the 3910 with him. Looking at modding the 3910 lead me to Alex Peychel of aplhifi. He has a reference level tube mod for the 3910 that has gotten some great reviews. In the course of discussing the mod with him, I mentioned the search I was undertaking for an amp for my N804s. He said that he did not like B&W speakers that much but had a friend who had 802s that sounded wonderful. He said the secret was an amp from a company called Spectron. They make a Class D "Digitial" Switching PWM mode amp which is kind of like a DAC at the front end to which gain is applied and then the analog signal is recreated in an amplified state through pulse width modulation. I thought this was a goofy concept, but looked into it a bit.
I talked to Toni Ulrich, who is one of the owners of Spectron and the husband of the designer, John Ulrich who founded infinity speakers. They are a very small company, and have some issues which I will discuss later. However, it turns out that Von Schweikert uses the Spectron digital amps as their reference amps. VS is actually very close to where I work. Toni talks to Albert and arranges for me to go to the Von Schweikert factory and listen to the amp. Obviously a completely different setup which consisted of VS VR4JR speakers (awesome by the way) Spectron digital amp, VAC Sandard pre, and Electrocompaniet ECD1 DAC. The sound was fantastic. Albert is super high on the Spectron amps and says he will use whatever amp makes his speaker sound the best. He says he has not found anything at all including things like a $60,000 Halcro that could compete. But it was in a tweaked out room with different equipment and speakers so I took it in that spirit. VS used the Spectron to voice the VR4 JR so if you are considering that speaker it is the perfect choice there.
In the meantime, Musical Fidelity was coming out with the integrated KW500 amp based on their KWP kilowatt monoblocks. MF boldy states that the "KW500 is one of the 5 best speakers in the world. It's that simple." Being as I really liked the A308 combo with the B&Ws I wanted to hear it. Found a dealer about 100 miles away that could demo it and also had the A308. This was with a Cary CD player and a set of Sonus Faber bookshelfs. The A308 sounded good. When he put the Kw500 it was an amazing difference. It was better in every aspect than the A308. They only made 500 of the KW500, so with some pressure from the dealer, and some haggling by me, I purchased it, thinking I may not have another chance.
The MF KW500 sounded very nice with the 804s. It had a good sound and tremendous control of microdynamics. Toni from Spectron called and I told her that I had purchased the KW500. She wanted to come down and demo the Spectron in my house. Since the Spectron sounded so great at Von Schweikerts I agreed since I did not want to wonder if I had made the correct purchase. I thought, in fact, that the KW500 would win out.
At the in-home demo, the Spectron was an eye-opener. It was more detailed, had a better soundstage, had incedibly fast and musical bass that made the KW500 sound bloated. It was just head and shoulders above the KW500. I was also hearing it through their Maestro pre-amp which they no longer manufacture. The sound was incredible. The KW500 was inside the evaluation period so I returned it and bought the Spectron and what sounds like their last Maestro amp.
Both are in my house now, and sound incredible. The best thing I can say is that it sounds so good that I don't find myself critiquing the sound at all. I just tap my foot and get lost in the music. Is that PRAT? If it is it has it in spades. It is incredible. Since, I have found a number of people who have discovered the special sysnergy between the Spectron amps and B&W speakers. They are a perfect match. I cannot imagine looking to replace them anytime soon if ever. Pete Watt who posts on the Asylum a lot as well, has 802s and uses the Spectron amps.
So that is my strong recommendation. I truly believe nothing will equal its performance. Over an audiogon, you can find some Spectron Musician IIs available and there is even a Maestro pre-amp there as well which is the combo I have. It also marries very well with a tube pre-amp so you could use something like the VAC, or Supratek, Conrad Johnson, Rogue audio all might match well. John Ulrich thinks the pre-amp is the best product he has ever made and I am incredibly impressed with it. If you could get the one on audiogon that would be a good choice. Or buy new from Spectron. You could probably convince Toni to make you a Maestro.
Now some caveats: Spectron does have some downside. There were a lot of quality issues with the Musician II amps. The units for sale on Audiogon mention this and those items should be fine. The new Musician IIIs are made by a new contract manufacturer and they say that all their production issues are behind them. Mine is performing flawlessly. Toni is a very nice person who goes out of her way to try and service customers. Unfortunately, in her zeal to do this sometimes she overpromises and fails to meet the expecatations she set. They are a small, cash poor engineering centric audio company and it does show. But the product is really unparalled.
For comparisons sake I listended to amps from Cary, BAT, Jeff Rowland, Krell, Ayre, Musical Fidelity, Arcam, Anthem, Plinius, Simaudio, Pass Labs, B&K, Rotel, and Classe. None compare to the Spectron when coupled with B&Ws. All are good and may sound better, possibly with other equipment than the Spectron, but for B&Ws there is a special connection with the Spectron. They are 550W per channel and stable to .2 ohms and this is a large part of the answer, since B&W speakers are much harder to drive than their published specs. B&W even admitted this to me. This was long, but hopefully usefull.