Car amplifier in cabinet - Strange high level input.

[Mikey]

I have this Majestic MA-8900 A Amplifier in a cabinet. Its line level input would be handy for CPS-II and the like, but I'd like to use its high level input for other games with amplified audio. The trouble is, it has this strange 4-pin socket, with a square, circle, square, circle pin arrangement for the L+, L-, R+, and R-. I've never seen this connector anywhere, and I can find no information about it on the web. I'd rather use the input directly than buy a high to low level converter. Can anybody help?

[brokenhalo]

can you post a pic of the socket?

[Mikey]

Here's that connector.