Another update. Construction is now complete.
I installed a heatsink on the regulator in the volume control board, that issue is now solved. I picked up a new voltage regulator board for the PSU from the kit supplier Conrad. Installed that and power is now working correctly.
I also picked up a programmable remote control on eBay for the price of a couple of pints to give me a smaller and rather more ergonomic remote control than the one that came with the Chinese kit. That is now programmed and working well.
Finally, I decided that rather than just splitting the output of the volume board to the output select board, the sub-woofer and cue-mix feeds, I would use a pair of “buffer” preamps to feed the sub and cue-mix outputs. I sourced a couple of stereo preamp kits from Maplin, modified them to allow use of the OMEG potentiometers for level control (as opposed to the kit’s supplied PCB mounted mini-trimmer pots) and have now installed these too. It should mean that the main output volume will not be affected by whatever volume I set for the sub and cue-mix feeds.
Here’s a few photos of the finished beast.