Update. Running direct into the ref 75 is a revelation in comparison to using the variable via the Truth. It sounds awesome - but.... Unless I'm going deaf in one ear there's a channel imbalance and no way of correcting it. It's consistent across CDs and very very obvious.

I've spoken to Resolution who say it could be a failing DAC chip (very expensive to sort out). But I need to do some experimenting - the Opus is the first source I've tried direct to amp and maybe the issue is the amp.

The reason I might not have heard this with the vinyl rig going into the truth is that the truth has no fixed balance point - so I might have unwittingly been compensating for the drop in volume on one channel.

It's easy to check if it is the cd - and I'll do that this morning.

It's also easy to check if it's half dead valves in one channel of the ref 75 - if it's not the valves then maybe the amp has a fault - which will really really piss me off and might not be easy to fix here in Spain.

If it's the Opus then I will be asking eBay for a refund.

Bugger