Unfortunately, Allofmp3 is not a legal site. IIRC, they are a Russian based site that was selling music without paying rights to the record companies. So they were selling stolen music. It would be as if I took my music collection and charged people to download it.
A way around the iTunes DRM limits is to download the song, burn it to an audio CD an add it to your computer from the CD. Then you can do with it as you please.