What you are contemplating is called "passive" bi-amping, since the crossovers remain inside the speaker. ("Active" bi-amping involves putting crossovers between the pre-amp and amp, then removing crossovers from the speaker - not something that the average person can do.)

In general, passive bi-amping is going to be comparable to using a single amplifier with the same output as the two amps being used to bi-amp (in this case, using a single 400W amp per speaker). I couldn't find much info on the DQ 20's, so I dont't know if going from 200W to 400W would be likely to make any difference. My suspicion is that the benefits would be slim at best. Since you have the amps, all it would cost you to test is a little speaker wire and a couple Y splitters, but I don't know that it'll do much.