Hi!
Yep - I'd first try the two in full-range mode, then go to the biamp mode.
When in biamp mode, if you're looking to get nice lows out of the 2 15's and good mids and tops out of the 2 10's, start with both amps at a volume level to taste, then adjust the crossover from highest frequency to lowest (adjusting counter-clockwise), and stop where you like the mids to come in.
I personally use the 800rb with 4 10's in the 300w amp, and another 2 10's in the 100w amp. I use it full-range, where the 2 10's are for my ears, and the 4 10's are for general stage volume/rumble.
I have gone with the bi-amp a few times and it's nice to have it as an option, but try them both for yourself!
Cheers!