Just a quick update on this in case this helps others in the future, its fixed!
Several of the capacitors on the internal PSU in the Amplifier Tile were failing, photos attached showing the ‘pregnant’ capacitors. I friendly local TV/electronics repair guy replaced the capacitors and all is well again! I guess like most modern electronics, there is a need for stable and clean voltages which the PSU was no longer able to give consistently.
Internally the PSU (green board) is seperate from the amp/DSP boards (blue boards) so it was easy to take out to send for repair, there are just a few cables to disconnect. Photos attached, again to help anyone else with similar issues.
Tom