hi m, the atmas are fantastic and are one of my very favorites!
not sure whether you know it or not but i also have two pairs of quad IIs which i have done work on myself. also a great amp but not quite as tonally neutral as the ma. i would suggest using a good tube pre with the either though. are you using a bam? if so, it should be buffered by the tube output section of a tube pre. it also has a capacitive input which is another reason to use it prior to the tube line output stage of a pre. you should also consider upgrading the speakers to the mme or mxe. that in itself would create a bigger and more important change than the amp upgrade would, imho.
regards,
bobby at merlin