If I didn't know any better, the OP sounds exactly like a conversation I just had about doing exactly the same thing, but with an amp that had two outs specifically to biamp, with a crossover.
Same thought process - running low freq's into the 115, and high freqs into a 210 or 410. Claims he did it, heard it, wasn't his, and wants it. I suggested searching TB and mixing cabs. Then I suggested if he likes highs, and lows, then get 1 cab that does both, like a 12/6 with an internal passive crossover. Or a 15/6 if he needs volume, etc.
Same thought process - running low freq's into the 115, and high freqs into a 210 or 410. Claims he did it, heard it, wasn't his, and wants it. I suggested searching TB and mixing cabs. Then I suggested if he likes highs, and lows, then get 1 cab that does both, like a 12/6 with an internal passive crossover. Or a 15/6 if he needs volume, etc.