The DOC, I believe, used the DX90 firmware and that makes it harder to remove. You might want to use the RKBatchtool and totally restore your system. That should let you start over fresh.
And I, too, am a big believer in SU 1.3.3. It's the first non-stock FW I heartily recommend. And was in love with 1.5.0.
My only issue is that I ripped my albums with no pre-gap, and while gapless on 1.5.0 worked well with those files, I find that SU sometimes cuts slightly into the first few notes of each song. And the idea of re-ripping does not appeal to me. But everything I am currently adding I am leaving with a pre-gap. Sort of a minor thing, it's just a bit annoying at times.