I assume pins 2 & 4 are line-level connections, so you should be able to connect a 3.5mm jack or RCA connectors.
Do you have a voltmeter? You might need to check the "normal" state/voltage of all the other pins. i.e. It might not work (or might not work correctly) with the other connections floating. Some of those connections may need to be pulled-up or grounded. Do you have a link to the full schematic?
But, it might be difficult to determine what "normal" is, since the main unit is not working. Is the main unit working at all? Are you sure it's not the amp that failed?
Does the amp get power through that 15-pin connector, or somewhere else? I don't see anything that looks like power, but there are pin discriptions that are not clear.
P.S.
If you can't get it working maybe you can buy small inexpensive, maybe something like this?
Do you have a voltmeter? You might need to check the "normal" state/voltage of all the other pins. i.e. It might not work (or might not work correctly) with the other connections floating. Some of those connections may need to be pulled-up or grounded. Do you have a link to the full schematic?
But, it might be difficult to determine what "normal" is, since the main unit is not working. Is the main unit working at all? Are you sure it's not the amp that failed?
Does the amp get power through that 15-pin connector, or somewhere else? I don't see anything that looks like power, but there are pin discriptions that are not clear.
P.S.
If you can't get it working maybe you can buy small inexpensive, maybe something like this?