Just wanted to dispel a forum myth.
I have used ATC speakers for about 5 years now. I have tried many amps with varying degrees of success.
I currently use the Michell Alecto Monoblocks, which I am pretty happy with.
This week a friend wanted to borrow my amps, so he loaned me his Nait XS. I wasn't expecting much.
However, as long as you are not wanting to blow the windows out, this amp is very capable at driving probably the most difficult to drive passive ATC speakers - SCM 20 SL's. The midrange is particularly special and as long as the volume is not too loud, but still up around 85db easily, the bass line keeps up too.
The sound is not as 'big' as with my Alecto's, but the inner detail is very nice with perhaps the odd high becoming a little hard, again with increased volume. Of course, ATC's have you reaching for the volume knob anyway, as they provide such a clean presentation.
So, I think for the average hifi listener who likes vocal, 'midrangy' material, this combo is certainly worth an audition and you should not be put off by comments around the net about ATC's need 150W + of power.
That said, I have heard my speakers with a Pass Labs X250. Wow, very impressive, massive control of the bass line, percussion was the best I and the owner of the amp has probably heard (especially from a such a small speaker). The amp was so good though, you really would want to stay away from badly recorded material, it rendered it near un-listenable - so I guess nothing new here from that respect, as you read this everywhere.
Personally, I would put the little Nait ahead of even the ATC in terms of an enjoyable listen.
I need to try it more with a wider range of music, but so far I am pretty addicted.