Tube amp

When someone says to me, "they are happy with their system", but are always looking to upgrade, this tells me, they are not happy with their system, whatever that might be. This is fine. The audio roller coaster never stops. Vertical biamping is when you have 2 of the same stereo amplifier, with each one driving just 1 speaker ( an amp channel for the woofs, the other for the mid/tweeter ). High quality y connects are available, but, you would need additional ics and speaker cable. IME, this gave me the best results. Horizontal biamping, as you are speaking of, is also common, but using a 2nd of the same amp is still preferred ( for many reasons ) imo/ime. Impedance, sensitivity and gain would be critical, for the 2nd amp, whether used for bottom or top. I understand the upgrade bug.

Most of the 801s I've seen work pretty well with tubes, although you need some power to make them go, but in that regard 100 watts seems like enough. We have several customers using 801s, mostly using our MA-1 amplifier. So that sounds like a pretty tube- friendly speaker to me.

I use a 38-watt tube integrated on enormous vintage B&Ws that are 91 dB efficient and dip to 3 ohms in the midbass.  The speakers were certainly designed to pair with high-current, high-wattage solid state.

The combo works for me, though I don't have a lot going on below about 50Hz.  If you can live without low bass and midbass slam, tubes may make you very happy.  My imaging and detail retrieval does not suck.

A friend of mine had his B&W 801s paired with Cary SLM-100 monoblocks (w/ Audible Illusions modulus 3 preamp) for many years. Not sure which series but this was at least 10 years ago, I thought they sounded great until he switched them with a pair of Parasound JC1 monos and we both agreed the difference was transformational. I don't want to say night and day but pretty darn close, especially for large orchestral music. Even listening to jazz trios late at night (after kids and wife are at bed!) at low volume had a bit more heft and sounded fuller.
Just one more data point, FWIW.