The C2200 is microprocessor controlled. One of the features this allows is the ability to trim each input up or down by 6 dB. Due to and error in programing the micro some C2200s were shipped where the trim could only be adjusted down. If you have a C2200 that does not allow the trim to be set at a + value the preamp should have the micro changed. This is of course a warranty repair so contact your dealer or McIntosh service.
Ron-C
Ron-C