Having had those monoblocks before, and dealing with Cary service before, you might find they'd say that one or both amps need to be re-biased.
Lower Volume from One Monoblock
Technical question on Cary 500 monoblocks. One amp is noticeably lower in output volume than the other. My sound was off-centered, a good bit louder on the left. Swapping the monoblocks left to right the louder sound swapped too. The left channel is now lower in volume. Any ideas on what goes wrong with a monoblock to reduce the output. The amp plays, it is just lower in output than the other amp?