I would definitely avoid pairing the NSD with the 3000. The phase response and dynamic capabilities don’t match up and I think it would be a mess. I do think you might be able to add a pair of pb1000 to the NSD though. It also wouldn’t hurt to get a umik/REW to measure the in room response, as subwoofers seldom perform their best where it’s convenient for them to be placed. And there’s also no guarantee that just adding a second one won’t make some frequency bands worse. You can use EQ but only to a point, and starting with positional EQ(best placement) is rule one.
FWIW, if you can play a long game, a pair of pb3k’s would be pretty badass. Buy one now, and buy a second as soon as you can.