I run xtant amps from that series. There are several possibilities.
first, look at the four module locations. You may have crossovers in there, the crossovers are on separate vertical boards. The crossovers should have a numbed SIP in them. If not, there should be two six pin jumpers at each module.
Check the input sensitivity jumpers. Should be a four pin jumper at each.
Note the input selection, 2ch or 4ch.
Passive in? Front and Rear inputs. Try the front inputs and front outputs. Passive goes through the high wattage resistors and is for rear fill, but the leads to the resistors can break easily. Verify the resistors are even there, large white blocks above the passive outputs.
Lastly, the amps are commonly found non working. Some have a thermal power supply issue, which is funny given the cooling, but the failed parts arent on the large heat sink.
Take some good pics of the board and I'll be glad to review and go over more tests.