I went from WHS to win7 and then win10 - each time a noticeable improvement. But I guess anything that can take LMS and soft squeeze. (I've never gone down the LMS route so I'm blank on that front).

You have plenty of ram (and I think that is the max the micro can take anyway).

I placed the SSD drive on the CD SATA bay so did not have to free up a regular SATA bay. (I did a BIOS edit so the CD SATA port operated at full speed but still much faster than a regular drive without the edit).

Just plug the Caiman SEG in with a good quality cable and play.

I doubt you can get a good quality half height coax or toslink card and anyway fitting half height cards into the Micro is somewhat a pain. One thing I thought of trying but never got round to is use HDMI for sound (but you would need to have an external HDMI audio extractor as well as an HDMI half height card). I think I have spare fanless HDMI half height card going spare if you are interested. Maybe your Micro already has an HDMI card?