A couple of thoughts...
Are you on a mac or pc? I don't know if that has any bearing on your issue, but I have only pc experience.
How did you record from your record player to a usb - what software? I have only used NCH Golden Records to accomplish this, recording from turntable > stereo > computer. (Obviously whatever you did must have worked since you can listen to the files via itunes.)
My personal recommendation, which might be subject to differing opinions, would be to record, and edit the tracks/files as wav files (on a pc) and then convert to mp3.
My uneducated guess is that your issue has something to do with mac compatibility, but then I am just guessing.
WavePad is a very useful and powerful software that I use regularly. But as I said, I generally work with wav files, and then convert to mp3 (if that is what I want.)
Anyhow, sorry that your experience has discouraged your view of the software, but I bet if you learn to work with it you will find it useful.