Oops, sorry, missed this post.
Ok, those of you who know me a bit by now have noticed that I recommend using dMC Auxiliary Input a lot over searching all over the web for futile programs which may or may not do the job.
Did you just say that you cannot play ATRAC files on your pc at all, using any of the players available? Did you also say it's the same as real media but with a different extension?
In that case, did you try renaming the file to a name with extension .ra or .rm, see if it plays in real Player and if so decode it to mp3 using dMC? You'll of course need to have the real player installed for that and the decoding will take place in real time (i.e. it will take as long as the song length).
But, as I don't have any ATRAC files myself, I can but speculate on this. In fact right now I have to go back and read this whole thread and others like it and see what's been said and done, because it's one of those very tangled notions.
What I have glimpsed so far is that you can connect your Sony mini-disc player to your soundcard through the line-in jacks and then you can use dMC Auxiliary Input (select the line-in or aux for input source for recording in Volume Control first). For instructions on how to use dMC Auxiliary Input refer to
http://forum.dbpoweramp.com/showthread.php?t=5362 .
I hope this helps.