Currently in MC you can simply select to push either a) Original or b) Always Convert. You must choose either one or the other, and there is no possibility to have different behaviors depending on the source media format. (The "Convert only when needed" setting does not actually do what you would expect here).
What is needed in a future version of MC is that, depending on the renderer playing capabilities, it should push Original for the formats that the renderer can play native, and push Always Convert for the formats that the renderer cannot play native.
In its simplest formulation, MC settings could offer the user a manual list of source formats, each with a drop down choice "Always Convert / Original" for the user to select from. (I think it would help to also offer the user a blanket choice to apply the "Always Convert / Original" to ALL of the source formats, but that's just a UI detail).
In a more sophisticated formulation, MC would add a button that would allow you to pre-populate the above mentioned "Always Convert / Original" selector list by running GetProtocolInfo on the target renderer, and parsing out the supported SinkProtocolInfo formats. The user could then manually tweak the settings afterwards.
( Note: for added flexibility, it would be nice, (but not strictly necessary), if Always Convert would allow different target formats than the PCM, WAV, or MP3 formats currently offered. )