Use Cheap Depot wire to run the Low freq. section, 12 gauge copper will be the same sound as just about anything honestly for the low end in this case...
Put both your amps back in stereo mode, one will be used for your left channel, and one for the right channel.. Now you have 4 Channels of amplification, use either of the channels to hook up your bottom end and the other for your mids and hi's, I am assuming you have bi-wire on the speakers, 4 binding posts total on each...
Now Run the Balanced Cables you have to the channel's being used for the Hi and mids, and the Bottom end with a cheap RCA cable from your left over RCA outs on your pre... This will have very little effect on your bass with the cheap speaker and rca cables, and not running balanced on those 2 less criticle channels to the bass is fine, trust me I have tried it and very difficult to justify all the extra money for better cables to run basically dedicated sub frequency volumes to your woofers or low freq electro panels.
Your amps will probably open up a little more running in the stereo config and sound a bit better balanced now that you have low end dedicated channels. This is verticle bi-amping, and believe it or not you might find less need for much tone control adjustment this way, but in mono you are making the amps work a little harder and basically not as clean in this scenario this is my opinion over just running the 4 dedicated channels...but you gotta try and it is relativley cheap to experiment and find out the better amp configuration...
And remember your crossovers create a lot more loss of power, at least the hi's and lows are feed seperate this way and have a better seperation on the frequencys that suck down the juice.
I have done similar testing with Mono vs. Verticle biamping, and found the biamping a bit better with the same amp, mainly cause I think that you are able to Tax the power supply when needed for more bass on one of the two channels vs. 1 single channel the whole time saturating the power supply continuosly.. I could be wrong, but seems somewhat logical depending on how bad the speaker soaks it up fast, plus this will up the efficiency on the channel running the hi's and mid's with cleaner seperated power and not being taxed by the bass simply takes less watts to feed.. so you could essentially get higher DB at lower volume knob for the top end frequencys. Gotta experiance it yourself to find out however, and not to mention I think I have noticed that the Heat(temp) of the amp will reduce if not running in Mono vs. stereo, but I do not have the amps you do, but have heard and owned Mcintosh and like the stereo style unless they are Monos period built that way, but I would not bridge mcintosh without at least trying the verticle biamp first.
