Stereo pre-amps with dual outs for bi-amping and a subwoofer line out

I agree with pkvintage. I currently triamp in an active stereo system and definitely hear the difference. I have removed the passive crossovers in my speakers.

In the past, with same speakers and tube amp I now use for midrange/tweeter, I tried biamping out of the preamp as you suggest, with a large ss amp for bass. Didn't like it at all.

BTW, in a setup as you describe all amps reproduce the full bandwidth, so not a good solution. In this case a bigger amp is generally better.

There are many technical reasons why active can be better. The key is implementation, as usual.
What you note is an alleged advantage of biamping and in my test it wasn't audible. Active crossovers, on the other hand, have proven sonically superior in my limited experience. And that was not with more expensive amps.

Do you use analog sources or just digital? I focused on digital and designed my system around that, so could take advantage of current technologies for actively crossing over.