I'm learning something new here (Single loudspeaker configurations and mono cartridges) really cool.
Not to sound like a broken record but I really would investigate further the reason for your preference - you might learn/discover something else. If you had a radioshack system then I might understand your unusual preference but with Sonus Faber Guaneri driven by Mcintosh preamp and power amp...I reckon you ought to get a fantastic stereo sound.
FWIW: Stereo recordings are meant to be heard that way. Certain effects are specific and unique to stereo and are used extensively in the industry. It is not just simple panning that is done but adjustments to phase which are made on most recordings to create soundstage width/depth/ambiance. If you convert them to mono then you will get some unintended effects.