I got the passive McOne directly from the builder in Israel. I had him convert the "mute" switch to a stereo reverse switch, meaning the left and right moves to the right and left. I also use the mono switch sometimes. The stereo reverse switch was worth the price of the unit (and there was no extra charge for the mod.) I have not noticed any shifting of the stereo image when changing volume and I do that a lot. On cabling, couldn't you just get some adapters, or go with unbalanced? For short runs it shouldn't be an issue.

Have you considered opening up your SM unit? For the price of a soldering iron and a new switch, you might be able to fix it.