In my experience, there will be a slight difference between Pro 2 Type-S and Pro 2 with Hypersphere's rings. The Type-S is a bit quieter (I've read that lubing can also make a difference, however, I haven't tried it myself).
If you need a quiet keyboard, a stock Pro 2 is not a good idea IMO. My girl friend wasn't too happy with the sound of the Type-S in the beginning, and much less the Pro 2 before I silenced it.
I'd say go with the Type-S if Hypersphere's rings are sold out (I'm sure more's on the way if you can wait), and if you can get it from Japan (the price difference won't be that big, compared to, e.g., elitekeyboards).