Chas and tmdip, I thought biwiring was different from (and theoretically inferior to) biamping. Biwiring as I understand it doesn't require two amplifiers per channel, jut separate tweeter and woofer connections on each speaker - but both feeding the speaker's internal crossover circuitry - so the high-pass filter (attached to the tweeter) can be fed by a different wire or cable from the one feeding the low-pass filter (attached to the woofer). But both cables can perfectly well fed by the same amplifier. Of course for biwiring the external jumper joining the tweeter and woofer binding posts, or whatever, has to be removed. The theoretical advantage is less interaction between the treble and bass signals in the cables. I run my Magneplanar 1.6s that way and I think they sound a tad cleaner, but I can't prove it.
Biamping on the other hand, at least real biamping, requires feeding the preamp's signal, via just one set of interconnects, to an external, line-level crossover network, and any such units good enough for high musical quality aren't cheap. (If anybody knows of good ones costing less than $500 could they tell me?) The crossover has treble and bass line-level outputs that feed separate power amplifiers, or separate sections of the same multichannel power amp, and the cables from those amps go direct to the speakers: no speaker internal crossover. Obviously this can't be done unless the speaker's own crossover circuitry can be removed or at least bypassed. In the Magneplanar line the two top speakers, the 20.1 ($14,000) and the 3.6R (a mere $4800) can be run this way (their manuals even tell how to set the external crossovers) but not my 1.6QRs. The advantage, which is probably more audible, is that intermodulation distortion in the power amp is virtually eliminated and the speakers are driven directly by the amplifier, without any intervening circuitry.
The financial benefit of biamping is that you can have a very high quality 5-channel system, with the left and right mains biamped, using a 7-channel amplifier - and the 7075 would have plenty of power for just about any installation short of literal theater size. The cost, of course, is that line-level crossover - but the cost difference between the 7075 and bigger 7-channel amps might cover that.
But you gotta have biampable speakers.