I run 602's with NAD C542 and C162/272. Can play as loud as my ears can stand with no distortion. Nad & 602's play well together imho, but we all have different ears.
When I say as loud as my ears can stand it, I am talking about ears approaching the mid fifties, more youthful ears may take more punishment, but every speaker has its limits. One must remember the 602's are rated at 125wpc on an unclipped program. I don't know what Carlos's Kef's are rated but it appears to me either his amp or speakers are clipping or his speakers are in dire need of repair/replacement.
my KEF q60 speakers can handle 100w each and are aprox. the same size as the b&w's and have a 8 inch woofer. the problem is that they are very old and i used them very much.
my question was if the B&W could stand a lot of volume without distortion and acording to My Rantz it seems they do.
Sounds like the NAD amp doesn't have the grunt for those speakers. I'm not sure that I would run a 320 with electronica. Try inserting an amp with more current into the system and see what happens. If you already tried other speakers with the same result perhaps it's time to try something else.