I've never really played with the media types, because I've never had an issue with any of my DLNA clients; all the media formats I use seem to be supported.
So I had a bit of a Google, and found some interesting stuff that I might investigate a bit further. There are three points of interest that I found reported:
i) Twonky supports transcoding (at least on QNAP devices)
ii) the 'Media Receiver Type' value has an associated setting file that may be modified.
iii) Twonky apparently added DSD support in v7.2.7. My devices run v7.2.9, so they may support DSD.
Here are some useful-looking links:
I'd never found the Twonky release notes before...
I had posted some comments on customising the Receiver Type, but never tried it myself:
Q. How can I get Twonky to provide full size artwork to media-playing clients?
I'm guessing the directory mentioned in a couple of the links:
on the MyCloud.
Feel free to report the results of any experiments you do.