I have never played this piece. So I can't give any technical advice on this specific piece. However, I have played other Rachmaninoff transcriptions, and I can say that if you're ever in a rut as to how to interpret something in the piece, almost all off Rachmaninoff's transcriptions for solo piano are recorded by the composer himself. This one included!
Also another thing with Rachmaninoff Transcriptions. I know this is really stupid advice because it applies to any piece, but for these Rachmaninoff transcriptions especially, it is IMPERATIVE that you keep a relaxed wrist. Otherwise you're just screwed. Some things are absolutely impossible to play in these transcriptions with tension in the wrist, especially in the Bach Partita, full of light sparkly passages that don't allow for any of the clunky sound you get when you have tension in your wrist.
So yeah! I hope that my words are meaningful to you, and I hope you have a good day and good luck practicing this rather difficult piece!