The Tidalis soundtrack is already fully high-quality sound quality and execution, etc. The remastering just refers to AI War, TZR, and then the new CoN stuff on top of that. It's a lot of work because he had to re-record a lot of it from scratch, remix all of it, make some adjustments to the underlying music to smooth out a few things that he felt were rough, work with new sound samples that are higher quality to get the most realistic sound possible out of them, and in the case of the electric guitar and French horn, arrange and record live performances of those instruments since we couldn't get anything synth-based that sounded nearly good enough.
Lots and lots of work, to be sure.