Biamp question

Buy-amping is an especially effective marketing tool for electronics manufacturers.  

At my current abilities I would be very hesitant to use an active crossover since I would actually have to get inside the speakers and disconnect built in passive crossovers in them. The nice 7 year Legacy warranty goes out the window and if I make a really bad mistake potentially a pair of $9000 speakers go south. I guess when I started this I was looking for an easy way to use these 2 amplifiers that would make a sonic difference without adding active crossovers and opening up my speakers. 

I have also read that when you go with passive biamping that since the crossovers being used are at the speaker level that the preamp still gives the speakers the full range of high and low frequencies. I can’t seem to wrap my head around that since one amp is going to hf and the other amp is going to lf. Seems like crossover of the speakers would prevent any upper frequencies from going to the lf and lower  frequencies from going to hf. Apparently the built in crossovers of the speakers cannot prevent that from happening in the same way active crossovers can? If that’s true is it because preamp sends everything and speaker crossovers can’t filter properly? And if that’s the case it would seem I would lose the implied benefit of the tube amp handling hf and ss handling lf. And I’m pretty sure I am the most confused person in the room right now. 

I bi-amped a pair of Legacy Focus speakers for years with no problem. I used the XM9 Electronic Crossover (marchandelec.com), instructions here Electronic (marchandelec.com). I used a Cary tube amp for the high frequencies and a Parasound amp for the low frequencies.  You pick the crossover frequency when you order the crossover. It’s easily changed if you like with a $10 chip. Easy-peazey. Only reason I went back to a single amp was because I downsized my listening room and the heat from the tube amp was unbearable (I live in FL). I don’t really miss bi-amping though since there are many great amps that make it unnecessary.

I do have one last question. I am assuming that both amps inputs go to the same preamps outputs. Is that a correct assumption?

Yes!