So I'm in line to receive six bookshelf speakers (all the same) (small, white Energy speakers - Encore?). I figured I'd put a pair in different rooms, connected to Airport Express', but they're not powered so I need to get an amp for each pair. They're not full range (presumably) but I don't plan on adding a sub. Just recycling stuff. I don't really NEED them - just want to use them. Aw, hell, I'm rationalizing. Any recommendations? Pyle, AudioSource, ...? I'm looking for something that I can leave on, preferably will power off automatically and power up when it senses a signal, doesn't cost much, and doesn't hum (or cause the speakers to hum).