I'm thinking no, unless there's a pre out that I'm not seeing in the Logitech page you provided, I didn't see anything resembling a 'line out' or 'sub out'
using it on any of the other outputs would just ruin your listening pleasure as it would unbalance your 5.1 (satellite surrounds only 'fire' when told to, so instead of getting the sound coming from behind you from whichever direction, you'll just get a sh*tload of bass from whichever satellite you sacrifice, then nothing until it's 'fired' again)
But look at it this way, if you REALLY do not want to break the sub enclosure, then one could simply 'live with the logi' for a little longer, and build the system you'd prefer, have more control over, and not to mention the power and performance you're looking for (in all honesty pc speakers will, in my opinion, never catch up to a decent set of bookshelf, or floorstanding speakers hooked up to a good amp, unless you buy a decent 5.1 audio system, sorry)
Sorry, forgot to mention
If you do try to get the Yamaha to work from the logi's amp
Will it work? yes.
How long for? Unknown, depends on how well made the amplifier circuit is.
Loud Volumes? Most likely, no, it'll probably trip what ever short circuit protection the logi amp has built in, or more likely, blow the Logitech amp altogether
(So in good conscience, I cannot advice that you attempt this option)