I don't see a problem with that...run the rear pre-out to the front main in as you are thinking. Don't forget to change the speaker cables also.
well i made the switch. rear volume was way louder, had to turn it down to 70 from 96 or max (100). problem was i picked up a loud hiss that did not increase with volume and pops when i operated the remote (volume control). i could hear the hiss from where i was sitting so it was unaccatable. i don't know what to make of it. i quickly switched back. it is dolby pro-logic if that makes a difference.
Oh? Do all channels have main-in/pre-outs? A few years ago I had an Onkyo receiver...I recall doing this and it worked fine. Once the amps are freed from their respective pre-amp outs...jumpers removed, it should work fine.
The rear pre section should not care which amps it is feeding to my way of thinking. Also, maybe you have a bad cable?