1. if you don't feel obligated to your dealer, check out sound by singeer, which is blowing out all the makers you're considering.
2. having owned various cambridge, nad and (currently) arcam, i'd opine that in general arcam tends to a fuller, heftier presence, while cambridge sounds more transparent and neutral; nads are also very dynamic and "full", though to my ears not as refined (and certainly not as reliable) as the others. as others state, you'll want to start with the speakers and perhaps have some sort of exchange right if the synergy doesn't work.