The sound quality from this headunit is spectacular, have got it hooked up to a pair of Focal 165 A1's via an Alpine KTP-445 Power Pack amplifier, which definitely helps with the clarity of the sound especially when the volume is cranked. No matter how loud its pushed it doesn't seem to reach distortion in the slightest.
The only issue I did have was with the USB input, firstly I tried it with a Lexar ECHO ZE (low profile drive) but it wouldn't recognise it, just says 'USB UNIT ERROR'. From searching the net is seems like a few people have had compatibility issues using Lexar drives in Alpine HU's. Have now bought a 8GB Verbatim Netbook flash drive which works perfectly and only protrudes out of the HU by 5mm - so there's no chance of it being knocked and snapped off.