Archive.org resource ISO Mega Link v1.2.3.0 BeatJam NetMD Drivers
Beatjam started as a separate piece of software but was adapted to add netmd functionality. The rabbit hole goes deep.
Beatjam (at least some versions) supports conversion from ATRAC to other formats, including in batch jobs.
At least one update can be found here, possibly a good source for others as well
News / Press Releases of features and versions of BeatJam:
https://av.watch.impress.co.jp/docs/20060116/dal219.htm https://av.watch.impress.co.jp/docs/20051214/just.htm https://av.watch.impress.co.jp/docs/20051207/just.htm https://av.watch.impress.co.jp/docs/20050418/just.htm https://av.watch.impress.co.jp/docs/20050405/just.htm https://av.watch.impress.co.jp/docs/20010214/just.htm