I am guessing that you mean converted the wma files. It would really be better to rip the original music again. Converting a lossy format to another is not really that effective.

That's why peerless mentioned the wav files, which are lossless

Incase your don't have better copies than wma, then take this as a learning experience.

There are BTW forums that discuss this keeping quality preserved while making music.

If this is electronica or similar that you are making, one comes to mind http://www.sectionz.com/home.asp It's a site for unknown musicians. It is possible to get a lot of tips there regarding the whole process from start to finished project.

Also you can upload samples to the site in Mpeg format