I'm not exactly sure what you're asking udo, but shorting ring to sleeve on a TRS plug is essentially making it into a TS plug. Perhaps this would be a cleaner implementation for you?
Also, there are 1 or 2 caveats about the MT 1/4" inputs. On the M-Audio FAQ, they warn not to use TS plugs into the 1/4" jacks if using the MT's phantom power, as this shorts the phantom power and can cause damage. However, their tech support told me as long as you're not using the MT's phantom power, TS plugs are OK. I wanted to know because I have an AT822 stereo mic. It's powered by an internal battery, hence no phantom, and outputs unbalanced on two 1/4" TS plugs.
Peace,
Sanaka