I beleive that's "technically" possible, but rather pointless and nothing really is made to "utilize" it. If you want to use two sets of speakers on the same channel, just get a Y adapter that splits one headphone jack into two
Oh fair enough, I just got asked that by someone. I mean I"m happy using a 5.1 surround sound system anyways, but my mate wanted to try using two systems... Crazy people lol. cheers.