Both do metal well but I think the D10 has a slight edge for metal. It has the faster bass out of the two. Both has punchy bass but it seems the D10 has a more quicker decay which matters for double kick drums. H40 bass dynamic is not the fastest
I mentioned earlier but both has good stage. NA1 is tuned to have that reference type definition. It has a slight cooler tonality due to the treble extension and detail. If your a treble guy or a macro/micro detail guy. NA1 will be enlightening for you.
The D10 has more in the way of bass emphasis vs the treble skew U fr tuning of the NA1. Sub bass on the NA1 is no weak sauce. Both might be similar there but since the D10 is not a treble biased tuning, It is more sub bass biased. D10 has a bit wider stage vs the NA1. Isolates a bit better too. NA1 is a more for discriminating detail oriented listen. The D10 is more you can listen to it the whole day, enjoy a punchy bass w excellent low end rumble, engaging and fun to listen to all day type of listen. Hope this helps.
Your getting an excellent premium cable with the D10 by the way. The NA1 has a gimpy noodle stock cable with a stiff ear guides that you will be able to feel behind your ears. This alone will make you want to change up the stock cable. Value= D10 wins in that category all day long.