I'm not trying to put rain on your parade, but aside from V&A, all of the Disney restaurants are family friendly. So finding a venue that is "quiet" and "romantic" might not be as easy as one would have hoped. In truth, you stand the best chance if you have a late dinner (i.e., after 8:00 pm) and choose a location that does not have fireworks viewing.
Of the Disney Signatures, I think you're best bets are Jiko, Artist Point, and Yachtsman. I actually really like Jiko and Artist Point. These three tend to be among the more quiet Signatures either because they're out of the way (e.g., Jiko) or just lower on the radar compared to nearby Sigs (e.g., Artist Point tends to get overlooked because of the other Sigs in the MK area).
I would also consider looking into the restaurants at the Swan and Dolphin. Many of the them get very good reviews and they don't take the dining plan, which does affect how many guests go there.