May I back up Recruit. You absolutely CANNOT bi-amp speakers with a single pair of binding posts. Each amp will see the other amp as part of the load and try to drive it. Unwise at best, messy at worst.
Biamping is where two amps are used for one channel. Each amp is fed the same full range signal which it sends to the speaker terminals. If the speakers are biwirable (ie four binding posts - which means entirely separate HF & LF sections in the crossover), the amp feeding the HF unit has the LF part of the signal filtered out by the tweeters crossover so only HF arrives at the tweeter and the amp feeding the LF driver has the HF part of the signal filtered out. The crossover must be able to be split in two (remove jumper plates) to allow this.
It follows that a three way, tri-wirable speaker is tri-ampable.
M&Ks for the most part, do not allow this. They are not unusual in this respect. They (and for instance ATC) have very high spec crossovers made to absolutely minimise phase shifts through the crossover region between the two drive units, to ensure even dispersion of all frequencies for all listeners in the room. It's this even dispersion that makes both of these manufacturers speaker remarkably non room dependant.
The ultimate extension of bi-amping is where the amps connect directly to the drive units and the crossover is placed BEFORE the power amps. This is Active amplification and is most excellent. The crossovers do their work on a much easier to handle line level signal and no power is lost as heat in lossy speaker crossovers. Active amplification always goes ALOT louder than it's specs will suggest.
I digress.
What you could do, if you really want to spend more money and it does work, is either use a seperate stereo amp for the front pair such as a RB-1080 or buy a pair of RB-06s and bridge them to perform as mono amps - one for each speaker. I'd suggest the former as bridging dosen't quite deliver what it suggests when speaker impedances are already low - M&Ks = 4ohm?
The main gains from going the pre/pro route such as you have, is the isolation of power supplies between the different stages of amplification, allowing each amp to work with an optimal clean supply of power of it's own, unencumbered and uncompromised by the demands of other amps. Separating the power amps is the next stage along this path. A loud scene using all five speakers will drop the power available to each of the other speakers being used. Powering the fronts from their own amp(s) will give an increase in headroom, reduction in distortion with the added bonus of improved imaging and seperation at all volume levels.
It may seem wasteful having a couple of channels going spare in the 1075, but the center speakers output will benefit and you could always go 7.1 with the spares.
Just a thought.
Russell