The music on my B2 is all in wav format. I loaded in stages from a B2 backup then used the BB1 to convert the files to MP3, it takes about 4 minutes per file so it is almost like having to play all of your collection. It took me the best part of a fortnight.
One problem that I had was when the BB1 became full and so was no longer copying over WAV files. It wasn't immediately obvious which tracks were missing.
At one point the BB1 locked up and wouldn't stop the conversion process, I had to take out the batteries and unplug the supply.