The Polk Monitor 30 does have two sets of binding posts on the back, so you could actually do this. With this particular speaker, i'm seriously doubting you would hear enough sound quality difference to make it worth it. Using a single AVR in 5channel stereo won't help much, most of those things are limited by their power supply anyways.
You cannot hook two amps to a single set of speaker terminals because the amps will see each other and usually blow up, blow fuses, or go into protection.
If you speakers have biwire terminals and you remove the jumpers then you can safely hook up an amp to each pair of terminals. This is called vertical amping (bi-amping has an electric crossover feeding the amps). You will need a level control on at least on amp to adjust the amps to put out the same amount of power for the same input (THX power amps are set this way with needing controls).
Can't hurt to try it. The improvement will not usually be power related but in some cases you will reduce the im distortion generated by the speakers feeding back emf into each other through the crossover. That is why biwiring sometimes improves the sound. If the amps are identical then you can also get and improvement by making one amp left, the other right and reduce crosstalk generated in a stereo amp that is not dual mono.
I was assuming the OP would have read up enough on bi-amping and bi-wiring before attempting to remove the jumpers... possibly a bad assumption to make. Either way, I have yet to hear a system that really improved with a biwire connection. (Mine included). Bi-Amping however, when done correctly, can make a difference, even to an untrained ear. I guess in theory, cheaper electronics could benefit from biwiring more than higher end, never really put that much thought into it.