I've not auditioned any senior MA speakers either but i know the B&W 704's match the Arcam amp and CD player very nicely.
What kind of budget are you looking at as i could also recommend the B&W CM7 speakers too. These are fantastic and work very well with the Arcam A90 amp and CD192 CD Player.
B&W seem to have a v good relationship with Arcam seperates. The A90 gives a good tight bass range, good midrange and crisp treble. However as the mag says, the A90 can seem a little vague sometimes, i nearly went for an A90 amp set-up but having had the Arcam Alpha 9 & 10 amps before, i went back to the Alpha 9.
I've got Acoustic Energy AESprit 309 floorstanders currently with my Arcam Alpha 9 amp set up along with my Arcam 9 CD player and theyre fantastic (also for sale... Cheap punt i know haha...)
Like you though i'm looking to go back to B&W speakers for this system.