Tube + SS bi-amping B&W 803 D3s?

Mixing amps like what you're talking about almost never sounds right. If you're able to try a tube amp without committing to a purchase, then do it. You'll probably need a crossover to get the levels right. I say fix the problem directly. If you really love the speakers and know you want to keep them for a long time, it would make more sense to get a more forgiving power amp and speaker cables. That said, more audiophiles have gone broke trying to get B&W's sounding right more than any other speaker. That's why most of us had B&W's and not have them. The midrange on your speakers is great. Fast, clean, articulate, etc.. It just draws you into the music. The highs are always a problem. Also, I wouldn't go by your memory of how they sounded when you first heard them at a dealer. Now that you've had the speakers for a while and know how they sound, hearing the original setup again may sound completely different. 

My own impression is to agree with 052rc's writing: "Mixing amps like what you're talking about almost never sounds right."

Here, there are some listeners who have found happiness with solid state, others who prefer tubes, and others who hop the fence from time to time. I would think that most here would agree that tube power amplification and SS power amplification are fundamentally different in character -- even those amplifiers at the highest price point and/or the highest performance point.

They are different; highs, lows, mids, sub-bass, impedance, phase, authority, slam, smoothness, stage, imaging, presence, air, on and on.

Bi-amped, approaching crossover frequency, one will hear two amplifiers contributing, more or less, the same amount of sonic energy. If the two sources of that energy are inherently different, then the result near crossover will be perhaps a strange amalgam. 

I'd wager some readers have found likeable combinations, but none without much consideration and many experiments. The probability of "picking" one SS amp, one tube amp, and one speaker, and getting close to excellent sound seems quite small.

YMMV; please do report back in detail. 

Cheers.

@emergingsoul A pair of McIntosh MC451 would be my dream for it but is a little pricier than I want to go. I’m sure your system sounds absolutely amazing though!

@052rc ​​@eurorack — Thank you both for the well-reasoned feedback. It’s a consideration but would be a very tough pill to swallow. Plus I love my turbine heads! 

The mixing of amps is indeed another variable, but I don’t think I’d go as far as to say it almost never sounds right.  It depends, and it certainly can sound right...and even better, which is what makes it enticing to try.   

The crossover frequencies where the amps pass off the signal, gain matching, polarity shifts, and the characteristics of the amps themselves come into play.  You might hit the setup on the first attempt, or at least may find some satisfying improvements, but if not there are still a lot cards that can be played to dial it in.  Tube rolling can make a notable difference, but the real changes can  happen if you opt to start bypassing passive crossovers and implement active crossovers or inline filters.  

Point being, you won’t know until you try.  If you’re willing to make the effort, there are some spectacular potential results to be had.  It doesn’t have to happen all at once to be a fun and successful endeavor.  One step at a time.  

My bi-amping started with two identical modified Dyna/VTA stereo amps  in a vertical configuration...one on the left, one of the right, and it improved the separation quite a bit, and the clarity somewhat compared to a single stereo Dyna/VTA 70 amp.  It still had the bass that a modest tube amp driving a 4 ohm load offers, so later on I switched to a horizontal setup and added an integrated amp to handle the woofers, while the tube amps fed the midbass and tweeters.  That led to me bypassing the passive crossover of the woofers and adding an active low pass crossover, which allowed me to adjust the crossover frequency and vary the gain....a notable improvement in bass and overall clarity to the tube amps and midbass/tweeters too.  The next step was to install an inline high pass filter to the tube amps to eliminate their responsibility of producing the bottom octave or two to the midbass...another very notable gain in overall clarity to the whole frequency range above that (~60hz).   All in all, it is considerably improved in several areas compared to just a single stereo amp....at least in my case.  Different situations, and likely different approaches required, but the potential remains if you wish to pursue it. There are typically solutions for every perceived issue. You’ll learn as you go, and can take it as far as you want to.  

@052rc the B&W tweeters can always be tamed down. Macs have a handful of hybrid bi-ampable amps.

@andrewmland try to demo AGD amps if you are spending in that ballpark. It's solid state but I hear the input section is tuned to sound like tubes making it the best of both tubes and class D but without the noise and replacement cost of tubes.