I'll probably catch hell for this, and you may not necessarily want advice from a guy whose car caught on fire from a wiring problem, but with a Sony amp like that, you could get by with 8 AWG. It all depends on how much you're worried about looks as compared to quality of installation. 2 AWG is big time overkill, and 4 AWG is still pretty big. If you can get a 6 AWG power wire, you'll be set, but 8 will work if you really want it to not show. (I've put in a 1000 watt eclipse amp with 8, and it did great.)
IASCA way overstates their standards, and Sony way overstates their power output, so its up to you.