All the compressors do not touch the audio in any way, they remain EXACTLY as per the original DVD.
As for compression with Shrink, anything greater then 0% is a degredation of picture and ONLY YOU can determine where it becomes to noticable, could be 1% could be 50% or more.
Personly I dont like any of the all-in-one easy solutions. They do have their purposes and will suit some people, but I find them to be all to variable in quality for me. If it a short movie, then generally it produces a resonable picture quality, but as it increases in length the output becomes utter crap. CCE produces a consistant quality output everytime, it just a bit more work to get there. Mention "work" and a bit of extra time needed and everyone flees back to the all-in-ones. They then convice themselves that the blocking, pixelization and pulsing are minimal and close enough to the original and can all be done under an hour.