Great little amp.
I needed a small amp to drive a pair of Fosgate P2D2 8" subs in a ported box. They are each wired in series to 4 ohms then paralleled to 2 ohms total. I started with an Alpine MRP-M500 (known to be a good amp) then bought the Sony XM-GS400 for my doors. I liked the GS400 so much that I gave the GM100 a try because it matched. I'm impressed. This little Sony does a great job. Better then the Alpine. Looks good. Sounds good. I don't like that Sony used the older style terminals though. They loose 1/2 a star for that and another 1/2 a star for the price. It's a little bit overpriced for a 600w amp but the sound quality may justify that for some. I mentioned the XM-GS400 4ch version. I HIGHLY recommend that amp for your door speakers. It's dead silent at idle (no hiss), crystal clear sound with a great soundstage and dynamics, and does every bit of it's rated power. The GS400 teamed with a GS100 are a perfect match but I'm not a real bass head. I wanted just a little more power to my other speakers (8" in the doors, 6x9" in rears) so I bought another GM400 and run them bridged.
Pros: Small. Clean power. Elegant styling. Easy to use.
Cons: Price. Uses old style terminals.