the NAD does not require a dac or an amp though it could use a little help from something like a Dragonfly V1.2 if you want to give it a little upgrade from your computer's sound card.
Magni can drive a LOT of headphones for its money but 1 thing is that NAD doesn't need an amp and that it doesn't offer the very best sound though it is capable of driving many headphones.
I did a bit of research on the Dragonfly V1.2 though I was still more inclined to pull the trigger on the M&M stack since I feel like it's more "futureproof" so when I'll do an upgrade or
simply buy another pair of headphones I, in most case, shouldn't have to upgrade the DAC/AMP side of my setup. I know I probably will upgrade it eventually but I just felt like I would
be able to keep the M&M stack longer than the Dragonfly.