Your original idea (bi-amping using the extra amp channels provided by the second five-channel amp) is an example of passive bi-amping. I'm by no means the expert on bi-amping around here, but I can give you a quick overview.

Passive bi-amping: split the pre-amp output signal and feed it to two amplifiers. This option can provide some more power reserve, but the concensus from some of the forum's resident wizards is that bi-amping with a pair of 100W amps is not going to offer much if any benefit over using a single 200W amp.

Active bi-amping: take the pre-amp output and run it through a crossover circuit to create two signals - a high-passed signal for the speaker's tweater (and possibly the mid-range driver as well, depending on the speaker) and a low-passed signal for the speaker's woofer. The two signals then go to two separate amplifiers, and the output of those amplifiers goes to the speaker. To make this work, you have to get into the guts of the speaker and re-wire around the speaker's crossover network so that the speaker connections go straight from binding posts to drivers. This approach offers the most practical benefits for bi-amping, but the knowledge required to implement it (both in building a crossover that properly matches your speaker and in bypassing the speaker's original crossover) makes it impractical and unwise for most of us mere mortals.

Bi-wiring: one amp channel drives one speaker, but two speaker cables connect the amp channel to the separate sets of binding posts on the speaker. The theory here is that your high frequency drivers don't have to deal with reflected "noise" in the speaker cable from the woofer. It's fairly common (I've actually got a few speakers at home wired this way as I type this), but again the resident experts seriously question the practical value in this arrangement. It's probably just as well to use good quality jumper wires and a single speaker cable as it is to biwire - especially when you've got to run 35 feet from amp to speaker.