This is bi-amping in a way, but as YOyo... said it's sort of weird that I'm using 2 channels.
Here's the deal on why I'm thinking about this. I'm on a budget and picked up 2 Athena as-f1 floorstanders. I'm considering grabbing a cheap klipsh multimedia sub off ebay to power them.... all my music comes off this pc and this way I can avoid paying for a dedicated amp at the moment.
Then I can up with the idea of using 2 channels from a 5.1 sub to increase the SPL. Additionally the 5.1 sub has volume control, which the 2.1 does not. I think this is going to be rather hit or miss given that I don't have much control over the sub cross-over point. The Athenas are 3 dB down @ 40Hz, so the sub won't add that much, but at the same time I'm hoping it doesn't completely filter out the lower frequencies.
I don't claim this is sane, but wondered if it might work.