The lucky owners of Vandersteen 7’s, for one. That speaker comes with a powered (via a solid state amp) subwoofer, and many 7 owners use a tube power amp for the upper drivers. People have done that successfully for decades, with speakers like the Infinity RS-1b, for one.
sfall, if you don’t have an external x/o splitting the signal into two or three sub-signals, you are sending a full-range signal to all the drivers---not a good idea! Are you sure you’re not just using a pair of stereo amps to in effect bi-wire your speakers? Bi-amping absolutely requires an external x/o, whether passive, active, or a combination of both. If an external x/o (external in the sense of not inside the speaker. A passive filter can be inside the power amp, on it’s input jacks) is not present, bi-amping is not, by definition, being accomplished. The outboard x/o replaces the speaker's internal one, splitting the full-range signal from the pre-amp at line-level and feeding the divided signal to one amp for the low-pass signal (bass), and one for the high-pass (mids and highs, typically), rather than at speaker-level (after the power amp---inside the speaker). Each amp then is fed only the frequencies intended for the driver(s) it powers. That’s the whole purpose of bi-amping!
Bi-amping with an active x/o (or passive) can be done vertically with a pair of identical amps if one so desires.