M-Audio AV 40 monitors. The only mentions in the manual are...
1. "Your AV 40 monitors have a variety of inputs for use with a multitude of devices. Soundcards or other devices with RCA line outputs can be connected to the RCA inputs on your left speaker's back panel. Professional audio devices with balanced or unbalanced 1/4" outputs should be connected to the 1/4" TRS back panel inputs."
(for soundcards and other audio devices)
2. "Connect the 1/4" or RCA input jacks to the corresponding output connectors of a computer sound card, portable music player, etc.".
So you see, it's rather ambiguous. I figured somebody here might have a more experienced or technical background on the subject.