In many audio enthusiast's understanding, there is no comparison between class D and traditional class AB audio. They would probably say that class D sucks and the those who use it have no discernment between good and bad audio.
However, I know others who are only interested in the basic music program and have no problem with class D or any class audio that presents a seamless, coherent sound that holds up to constant high SPLs and long hours in high temperature environments. Perhaps that's more what you are after.
Class D will waste much less power than class AB, will have significantly smaller electronics and it should be much cheaper to buy modules, heatsinks and power supply for. It seems ideal but if you are really after the best traditional quality sound, you might not want to go that way. If the sound "quality" is not necessary for your interests, by all means save some cash and effort with a quality class D purchase. If you want the best possible from your DIY efforts, then go with the class AB amplifier modules. Don't forget to visit the Class D forum here for a better perspective on the available products.
I have no great problem with Hypex products that I've heard, including "high end" modules. There are some areas in the attack of the sound that can even surpass standard AB amps but overall, I'm reticent to change what I'm happier to listen with when playing serious music.
The amplifier modules are only a start in the process of amplifier building so for either case, concentrate on the best power supply and wiring arrangements you can afford, this being the other and expensive half of your amplifier. Whilst the supply, apart from the transformer is included on NXV101, You need to make your own arrangements or purchase a power supply(s) for the Hypex, so it may not be as good value as it seems.
I would add that a DIY SMPS power supply for audio means the amplifier circuit is connected to mains and working on it is technically unsafe practice.
IOW, we don't condone it without an isolating transformer between mains and power supply. It makes it rather more expensive then.
As the 684 speakers go; I think these are great value speakers, fairly sensitive and probably have a lower impedance that promoted - more like 6R with a dip to 3R. They certainly don't need a powerhouse to drive them so unless you want to test them to destruction, I think 100W/8R is ample power for them, assuming that translates to more like 170W at 4R, as a solid power supply should permit. For EDM however, I would be looking to bigger bass drivers for solid reinforcement - Perhaps a subwoofer can help out.
What you actually use as an amp. for the main speakers is down to what you have available and the power is not really important as long as you have enough and a safe means of limiting it to keep your system out of the repair shop.
