As I have mentioned I found the biggest difference between the NSD and any of Axiom's subs is that textured sound Axiom has.

So far as output, the EP350 is slightly less than the NSD and I feel the NSD is only slightly less than the 500 and this is all only really noticeable with A/B tests I have done. They are all very good subs.

I actually prefer the sound of Axiom's subs to my PB13 but I liked the low 15hz I could get out of the PB13 for the odd movie scene.

Jason
M80 v2
VP160 v3
QS8 v2
PB13 Ultra
Denon 3808
Samsung 85" Q70