I haven't done much converting in this exact manner, but I do a good amount of DVD authoring. I actually didn't like TMPGEnc's DVD Author program very much. These days, my VIDEO_TS folders are created through DVDlab from Mediachance. After importing videos into there, it will warn you of any compatability problems, and correct many of them. However, I still use TMPGEnc to get my files
to the correct format for importing. But if you've got MPEG2's already that shouldn't be a problem.
Also, it might be good to check out
DVDRHelp.com to make sure you know what your standalone player is capable of playing.