System OK? Opinions?

You'll see a lot of different opinions about amp quality and there are so many different brands that it's hard to get any group to agree on a good amp, but that one you linked is in the right area in terms of RMS wattage (about 350 to each sub at 2ohms) and the rest of the specs look pretty decent I can't speak on the brand though, maybe somebody else has experiance with them.  In terms of using the Sony amp for your speakers, that's a great option.  In general, it's best to stay away from sony, but since you already have the amp, it wouldn't hurt to hook it up to your speakers and you'll end up with better sound.  I'm not saying you should expect the amp to last that long but you'll probably end up getting more life out of it pushing speakers than you would trying to use it to push subs.

Way to actually listen to advice, that's a pretty rare thing.  Good luck.