I also bi-amp, but my speakers come with an active outboard crossover splitting the bass and treble signal at about 200hz (it's a 4-piece system). The only things I'd like to add to Ljgj's fine post are that (1) the input sensitivity of the different amps will also play a role in how loud they are vis-a-vis each other--you'll really need a way to adjust the volume of the two amps, whether through an active crossover or perhaps some passive attenuators like EVS makes; and (2) depending on the crossover frequency, the sonic character of the amps you are using can make a difference (I have switched bass amps recently because the new ones are a little faster and leaner in the 200hz region, making for a better transition to my tubed amps on the top; I might not be so concerned were the crossover at, say, 50-60hz); you'd like to get amps that make the crossover sound as seamless as possible. It can be difficult and may wind up costly to do the biamping; I don't think I'd have done it were my speakers not set up for it.
Tube/Solid State Bi-Amplification
I've read about people bi-amping using solid state for lows and tube amps for mids and highs. How is this practically done? I have bi-amp capable speakers but I only have one input on my preamp. What additional equipment would I need to buy and is it readily available? Not to mention, are the results worth all this effort? Has anyone done this??