So after trying to get my system going I've got the CD drive working (had crud in the gears) however still zero sound. Pictured is my board
http://i66.tinypic.com/c0rrm.jpg
Ugh, no fun working around the gamedoctorHK region mod.
Anyways, there could be a number of reasons why you have no audio. However, being that you have no audio at all I would check the 4558 op amp just to the right of the AV jack. Lots of times old cap goo can get underneath these and short things out. The contacts can also corrode. 95% of the time the op amp can be removed, contacts cleaned, then re-soldered and all is good again. In some cases new leads/wires have to be soldered in to fix corroded contacts on the board and in more rare cases the op amp has to be replaced. Also, check that the op amp is getting around 3.8V from the 22UF next to it.