Most Arcams have a fairly neutral signature, detailed and the midrange is sublime IMO, although not heard the A19 as yet. Can't see it being any different from other models, though.
Have heard numerous Nads over the years, and they demonstrate plenty of power that's a good match for the MAs. However, for my tastes, they can be a little bass-heavy. Arcam doesn't have the powerbut IMHO they are better balanced between the frequencies than the Nads.
Both Nad and Arcam are very good matches for the MA Silver ranges.