I can say little more than I personally like the BX2's. Their tweeter (shared with the Radius, Apex and Silver ranges) is sparkly, spacious and hits a lovely balance to my ear. Piano notes are perfect.
Marantz amps are known for their relative warmth compared to other manufacturers, so you seem to currently have a slightly warm amp running slightly warm speakers which is exacerbating the effect. So your choices to pepp things up a little are to introduce more forward speakers (like the BX2's) or a more peppy amp (like the Cambridge 651A for example).
The BX2's are well made and usefully front-ported so aren't overly fussy with positioning. But I would still recommend bothering to take your amp to your local Richer Sounds and listening to the combo for yourself before parting with the cash. You might also consider KEF Q100's which are more forward again should the MA's not have quite enough sparkle for you. Their treble can be a bit too much for my taste, but your Marantz might just smooth out the treble nicely.