I own one of these, and all volume issues were solved by the spacer modification mentioned to the lid allowing heat to escape.
I have the Omron 'patch' and I would experience volume fine at one db level, next one up ~+10db in right channel, next click fine, next +10db etc. It's like betting on 'odd' in roulette. One day I even had one channel out, fixed by advancing to the next click on the ladder.
I'm convinced this is purely a heat issue - that is until I run into issues from the relays being in the 'on' position for extended periods - if that is an issue, hasn't happened to me.
But can report all has been remedied with spacers, and flawless operation since.
How could Cambridge Audio overlook this obvious engineering factor? To go through the trouble of such an elaborate volume setup; terrapins! Only not to factor how hot the thing gets with the transistors and heat sink - like a toaster oven on 'keep warm' setting?
These blokes also work at Jag?
And make sure it's TIGHT! with foam tape around the opening of case of the lid - ensuring heat retention. It's asinine.
I took 5mm in height rubber grommets, put a tiny dab of super glue and affix to the underside of the lid to hold in place. I then had to upgrade the screws to a longer M3 - M3 12mm to be exact and fastened the lid on, leaving about a 3-4mm reveal all the way around.
Does it look perfect? no, Does it look bad? no, is the fix smarter than terrapin? maybe.
100% reversible, 100% no longer a pizza oven, and most importantly volume perfect. It might be placebo, but it might even sound better..
Tip for readers/owners of the unit, it's a must-do mod I think.