I have this kind of issue.
When I plug my phones (I tried 2 models) or CD to "CD/MP3 in" the output signal is very low. The volume through headphones or PA is at least twice low as my guitar signal or usb stream from the computer and it's almost gone when line/amp selector is down (when I turn off boost)...
even more, the vocal sounds nasally and muted, kind of voice-cancel effect, and overall sound is not natural and "closed".
I have a latest firmware.
I can also admit a kind of reverb effect
What can you say about it?