Hi Douglas,
After reading extensively about the newer technology of class D power conversion modules, I developed a strong urge to audition and compare the various modules in my own system to hear how they compared. My original thought , just as you seemingly decided, was to have a pair of Hypex nc400 mono-blocks built.
However, during my reading I discovered there were a few highly regarded alternative modules developed that had the potential to outperform the unanimously praised Hypex modules, namely the Abletech and Pascal modules utilized in Marten and Rowland amps respectively. But, at this point, I hadn't actually heard any amps using any of these modules. Also at this point, there was little to no online information comparing these modules. This lack of info was the reason I started this thread.
After reading many online descriptions from Hypex amp builders and owners, I began to believe I knew the performance I could expect from Hypex nc400 monos; very good power, very low distortion with a very detailed and neutral presentation. Then I received feedback on this thread that the nc400 based amps are very good but not in the same league as nc1200 based amps (like the Merrill Veritas and others). That's when I decided to have mono-blocks built using the Abletech ALC-1000-1300 modules. My thought was I could play it safe and get very good performance from a pair of Hypex nc400 monos or I could take a bit of a chance on the potential that the Abletech module based monos might perform even better.
Earlier in this thread I documented my long path to actually having a pair of monos built using the Abletech modules, in case you'd care to know the details. Long story short, Dennis Deacon at D-Sonic put the 2 Abletech modules I bought into 2 of his cases and delivered to me, in affect, a pair of his M3-600M mono-block amps.
I've been using them for a few months now and I'm thrilled with their performance for both music and ht. The 1,200 watts/ch (into my inefficient 4 ohm Magnepans) results in an effortless presentation that is very detailed and neutral but very musical with good recordings.
I can't state that they outperform the nc400 amps because I've never heard them in my system or any other system. I would guess, based on users' feedback, that they have similar qualities as the D-Sonics.
Your choice may come down to which is a better match for your speakers in terms of power required. The D-Sonic M3-600M are 600/1200 watts into 8/4 ohms respectively. The Hypex nc400 are, I believe, 200/400 watts into 8/4 ohms respectively.
I hope this helped a bit,
Tim