The amp will probably have outputs that have direct wire connections (assuming using a Lepai or something), so your only roadblock is finding the connector that mates with the speaker connectors. According to the Pin2k schematics, the board connector is the HDR Mini-Fit JR R/A 6 Pin header, so you'd need the compatible plug.

I also remember reading that the pinout was labelled wrong on the schematic, possible something about one of the speakers + and - being reversed, but that should be easy to figure out.

With an 1/8" pc out there is no reason to recreate that board. Tap 12v from the computer PC using a molex for a car amp and just figure out that tiny molex speaker connector.

From the PC power supply I've tapped the 5v for the CRT video amp and the 12v for LED backbox lighting with no issues.