Did you resolve the issue with your Ashdown? I've had a similar problem with a new ABM500 Evo III. I set it up with an ABM 1x15 cab in the house, played at low volume for 5 minutes when the sound cut out. Signal still getting through, VU meter moving etc. Tested the speaker and found it had blown. Relieved it was the speaker rather than amp, I sent it back for repair. Subsequently used amp with an Ampeg 2x10 classic (300w, 8ohm) at a gig. Half way through the 1st half the sound cut out again. Could continue as signal still going through DI and into pa. Tested speakers again and found they were blown. The shop has now taken the amp back for a "repair".
On a side note, does anyone know where I stand legally if the amp I bought was faulty and has blown a cab I already owned?
Cheers!
Dave