Finally got my amp working again!!! Ended up with three non-functional DSP-boards (bought two used cards on eBay + my original board). With one of the DSP-boards installed I could connect with FUSE so I reinstalled the firmware but still no sound, but it was possible to change channels and the TAP-LED was blinking. So I decided to try reflowing the board in the oven. 10 minutes at 200 degree Celsius (about 390 degree Fahrenheit) and then let it cool down for 15 minutes. Installed the DSP board and now the amp is working again ;-). The two DSP board that I have left seems to suffer from some other problems since it isn't possible to connect with FUSE and no LED's are working. Tried to heat up one of the boards but that didn't help. Hopefully I'll find someone who is good at repairing digital circuits since these cards are hard to find in working condition.