I have no experience with the Mu-so but looking at the spec sheet, it features two inputs:
- optical (TOSLINK)
- mini jack
If you want to plug a turntable, I can think of two (relatively cheap) ways on the top of my head:
- a phono amp with TOSLINK output (such as http://www.thomann.de/intl/art_usb_phono_plus_ps.htm), a pretty rare beast;
- a phono amp like http://www.thomann.de/gb/behringer_pp400.htm (cheap and pretty good) and connect it with either a jack to minijack cable or a stereo RCA to mini jack one.
If you go for the RCA to minijack route pretty much every single phono amp will work.
I don't know of any turntable that comes directly with a TOSLINK output (some Stantons and Denons have S/PDIF ones).