AFAIK, the Oade Bros provide a single mod - W, P, or T. Never heard of the "combo" mod before.
If yours is truly an Oade digi-mod, you have a choice: send it in for just the W, P, or T mod, or send it in for the W+, P+, or T+ mod. The latter makes sense if you can swing the cash now and would otherwise have gone for the + mod later. The + mod is especially useful if you record sources that require high gain - the + mod makes the UA5's self-noise very, very quiet (not audible to my ears) even at high gain.