Musicmatch maintains its' own database in it'sown format. We (a couple of us at work) stopped using it as we could not get a commitment from them as to whether they would be able to convert their format to standard ID3 or even ID3-V2.

We are currently using Audio Catalyst (Xing) and MP3 Producer(Fraunhofer)

Both of these produce correct ID3 tags

Kamau Wanguhu