I have a dvd similar to this non-sequential multi-pgc title setup, which makes use of NextPGC and PrevPGC. It does not use post command "Link PGC x" but rather "Jump Title x chapter y". So try this:

1. Add post command "Jump Title 1 chapter 2" to PGC 1, with NextPGC=2.
2. Add post command "Jump Title 1 chapter 8" to PGC 2, with NextPGC=3 and PrevPGC=1.
3. Add post command "Jump Title 2 chapter 1" to PGC 3, with PrevPGC=2. You mentioned that you redirected this back to the main menu. That's fine. Just thought you might want to play the next episode.

Do the same steps for PGC 4-6.

Suppose you're on PGC 4 (Title 2 Chap 1) and you want to go back to Title 1 Chap 8 (credits). Then you must

1. Create a dummy PGC 7. Assign it to Title 2 (RC on PGC and "Assign to Title").
2. Add pre command "Jump Title 1 chapter 8" in PGC 7.
2. Assign PrevPGC=7 in PGC 4.

You can use free version of Rebuilder and HC (freeware) as the encoder instead of CCE basic. The difference is the encode time takes longer. Rebuilder Pro has more options. It'll be worth your investment. Rebuilder is not a ripper. It is a frontend interface that makes use of other free and commercial encoders, which do the real work. Rebuilder determines bitrate distribution for each segment, and is very configurable.

You can use RB-Opt utility to assign a lower bitrate after doing the Prepare stage from Rebuilder.

Just check, Recode compresses based on PGCs.

[Edit]Don't use Showtime. It does not honor NextPGC and PrevPGC somehow. WinDVD and PowerDVD do.