Let's say I want to bi-amp an Altec 2-way setup or even a duplex.

Using either a passive or active XO, I'll need two discrete amplification paths per channel.

I've read that generally speaking, old (circa 1960's) HF compression drivers will do better with tube amps (high output impedance), while the LF drivers will be fine with solid state amps. Do I have this right?

If these distinctions don't really have much of an audible difference, it'd be easier if I had a single amplifier with four discrete channels, so I could basically just use one amp. Plug the source into the XO, the four outputs from the XO into the amp, and amp to drivers.

Is there such a thing? Most bi-amp set ups I see are independent stereo amps for LF and HF.