There is no converter that can transfer DRM protected media files to your PSP. Xilisoft PSP converter is of no exclusion.

You should remove DRM protection from your iTMS AAC music files first. Aplle iTMS DRM removal software works with iTunes 3,4,5 and 6 (although free lossless DRM removal software like jhymn, hymn, ourtunes, mytunes, sharpmusique works with iTunes 3,4,5 only so you have to buy music with old version of iTunes to remove copy-protection with them).

After removing DRM protection you may use an audio/video conversion software like AVS Audio Converter or Replay Converter.