A&R again (bet you're all getting bored of this one)!!

I'm the proud / stupid / poor / seen off (delete as you feel appropiate) owner of a pair of A&R A60ap and SA60x active amplifiers. (Thats 2 A60s and 2 SA60s!!)
One pair (integrated + power amp) works, but with a volume difference between the channels of the A60, this I expect will have to be returned to Arcam, as recommended by you guys, for a service which will hopefully sort it out.
The other pair do not do anything at all! Ive run the A60 with my working power amp, and it still didn't do anything. When I checked the fuses (tested before switching on, and definitly okay)after testing like this, they had blown, yet (except the illumination of the LED) the amp appeared to do nothing. The pre-amp section works, and outputs to the SA60 power amp (as one speaker works when its tested with a working power amp), and Ive tested the power supply and it seems okay.
Likewise the non working power amp, when tested with my working integrated allows a signal to pass into it, through the crossover board, and back to the integrated - it is just unable to drive the speaker that connects to it.
I'm sure everyone on this site is getting sick to death of questions about A60s, but if anyone can give me any ideas about what could be wrong it would be much appreciated (basically I can justify sending one pair back to Arcam, but not the other - if the worst comes to the worst I'll make a pair of gainclones out of them using the circuit on Decibal Dungeon, but I'd like to get them working if at all possible).

Cheers