There is a drop off in both the quality and volume once a track is edited and moved to the mix editor. When I play back the track edit, the quality sounds great. I play it back through the mix editor with other tracks, both the quality and the volume has decreased greatly.

Any ideas?

Are you creating a mix with multiple tracks so you can overlap them? If so, then Sound Editor decreases the volume of each track so that the final mix won't have any clipping in it. The "quality" should be essentially the same, just volume is reduced. After you export your mix, you can then bring that back into Sound Editor and select the "Maximize volume" option (I'm paraphrasing, I don't have it in front of me) to bring the volume back up.

Hope that helps!