Symphony MP3 issues?

Ive only had my 08' Octavia VRS a few weeks now, and finally got around to trying out a few mp3 discs in the Symphony head unit and multichanger.

For some reason, it only plays so many of the tracks on the mp3 discs i have tried out? For example, one of the discs was basically a 4 disc Ministry of Sound compilation reduced to one mp3 disc. It only finds, or lets me play a third of the tracks on the disc and shows two files at the top of the display?

Secondly, i take it the 6 disc multichanger does not play mp3's as when i tried, the Symphony displays 'cd rom' for each disc loaded and refuses to play.

Any ideas?

Cheers

S.