This is not a subject that I know much about. This forum is for programmers, and I suspect that you are not a programmer yourself - excuse me if I am wrong. You say that your files are from a CD but you do not say what the file format is - I am imagining mp3 because that is the most common. In an mp3 file the music data is stored in groups of four bytes - two for one channel followed by two for the other channel. If one simply (?) rewrote the data by copying one pair of bytes to replace the other pair then the same sound would come from both channels, which is what I think you want. You would finish up with three versions of your music file - the original two track version; one with the left channel repeated on the right channel; one with the reverse.
This is would not be technically difficult for a programmer who has previous experience of working with mp3 files, although it is a little more tricky that I have suggested here because there is more than one mp3 format, and the data is divided into frames which can themselves vary in type, but usually don't.
We will have to see if anyone joins the conversation with a better idea (or more knowledge). People on this forum are very generous and have many skills that they willingly share.
