I haven't heard any of the Hypex stuff yet but I am inclined to suspect it is very good---the UcD (licensed from Philips) concept is beautiful. Way way better than the "pure digital" phoolery/marketing hype madness. The only drawback I can see at first glance is the difficulty of avoiding heterodyne artifacts with multiple channels in a system, unless you carefully choose the output filters' natural resonances to be spaced well apart from each other, and then customize the details of the feedback network appropriately. Or, do other games that explicitly synchronize and adjust the effective output filter resonance on the fly, which is decidedly nontrivial.
IMO the National stuff is nothing special---big power op amp approach that is o.k. but nothing to write home to mother about. Also, not very efficient and really ugly when it starts to protect. And yes, it is difficult to do better and especially when you want the result to be bulletproof---but whoever said this was supposed to be easy anyway?
