I read:

UserTracks added. Now you (or others) can make your own RealTracks (guitars, pianos, strings, etc.). To make your own RealTracks, simply record tracks in Band-in-a-Box, RealBand or any DAW, and name your UserTracks, and add them to the UserTracks folder in Band-in-a-Box (or RealBand). They are now ready to use, the same as you use other RealTracks!

Does it mean that I have necessarily to RECORD a track?

OR

...(since it's written that I can use any DAW), could I use any wav file, even existing one?

An example: suppose I have single backing tracks for an existing song (e.g. Money for Nothing, Dire Straits). Could I use the bass, or the rhythm guitar of that song to make a UserTrack, and then use it in any new song with BIAB?