Have you tried this:
1. merge the movie from the 2 discs to one file with a prog like Avidemux, Virtualdub or a similar one
2. merge the two srt-files in SubtitleWorkshop to one file
3. test with a Prog like VLC-Player, who shows automatic the subs, if they have the same name as the movie-file (of course without the extension
) whether they are synchronous
If the srt is sync with the movie, you have what you want.
If it's not sync, you can adjust the subs and the movie easy in SubtitleWorkshop.
"I don't believe in God. I just believe in Billy Wilder" - Fernando Trueba