Is it possible to decode DMR using a SignaLink and a plain old analog radio (in my case a Kenwood TM-V71A)? I had a hunch that people must have been doing it otherwise what was the point of software such as DSDPlus and MultiPSK? Both of these pieces of software claim to allow decoding of DMR (and P25, D-STAR, NXDN and other modes) using a sound card interface which takes the audio out from a radio into what looks like a "line in" or "microphone" on a computer.
TL;DR - The results are disappointing so far, but it doesn't look impossible to achieve. Next steps for me are to improve the signal quality into the radio. The steps below I think have maximised the quality coming out of it.
There are a few key lessons I learned in this process. This will save you a lot of time as this info isn't neatly assembled anywhere else that I could find: