Biamping, bass and amplifier type.

I agree with Bob, save yourself the cost of an additonal amp and get a quality subwoofer. A subwoofer will produce way more bass than a biamped speaker.

I've biamped in just the way you're considering: a ss amp to the bass cabinets of my vr4 iii's, and dynaco mk iii monoblocs powering the mids and trebles. Though my ss amp puts out 170wpc, and the Dynaco's are rated a 60w, gain difference is not an issue b/c of two convenient configurations in my amp and preamp: 1) my ss amp has volume pot (per channel, but a single pot controlling both work just as well); and 2) my preamp has two sets of outputs. Those aren't requirements by any means, but it makes bi-amping a cinch. I keep the volume pots on ss amp at about 4, and then leave them alone; everything is controlled via the preamp, and I don't notice any imbalances across the volume range. And with the VRiiis, which get down to about 20hz, no subwoofer need apply.

I disagree with Stewie. He's gotten lucky with gain. Many amps will increase at different rates. Some amps will double output with a quarter turn while other only go up 10%. There is no way to compensate for different rates of gain.

There are 2 main types of potentiometer. Linear and Log.
They both may start (50kohm, say) and End, (zero, hopefully) but get there in 2 different ways.....'slopes'. They will only match resistance at those 2 points based on rotation.

As for bi amping, I have never heard a discussion of amp latency....that amount of time a signal takes to go THRU the amp. If it took JUST 1 millisecond longer for the signal to go thru the hi frequency amp, that would be like pushing the mid/hi drivers over 1 foot back. (away from listener)
This would start no end to problems.....smear of image, phase problems and more. The holocaust at/near the x-over frequency would be awful.

Before you toss this one in the round file, think about people who are good enough / discriminating / well eared enough to hear which way a fuse is installed.

My speakers are bi-amped. I run out of my preamp into a dbx Drive Rack PA. From there I go to a JRDG 102 amp which drives compression drivers through horns. The other amplifier is a Perreaux PMF 1850 driving 15 inch JBL woofers. Since the drivers are so different, what would be gained by using identical amps?
I gather that most of you are talking about using the inboard passive crossover for bi-amping. Is that correct?

You might want to consider a Drive Rack instead. Just bypass the native crossover and hard wire your drivers to the respective amps. Every parameter can then be modified by programming the dbx including time delay between drivers. There is a learning curve but if you like to fiddle around with your equipment, this device will open the door to infinite possibilities.
I got mine from Amazon and the price was very good. The pros advised me to go this way rather than Behringer.