Yes, I do the same thing. I have a cord with a Mini-Stereo Plug (3.5mm) to a pair of RCA connectors. The mini-stereo plug goes into the Mini-Disc usually into the Line-In (White) jack. The other end can go into the jacks on just about any piece of audio gear. I also have adapters to fit this end to go into just about anything else. Most common is the 1/4" Stereo Phone Plug. With those two, I can plug into just about any audio soundboard and go directly into the mini-disc.
Now on the Mini-Disc recorder you can either set it as automatic recording level or manual. I usually use Manual level, and then adjust the level out of the soundboard to get a good record level.