I used to own an NX-1000, and it took a beating and kept coming back for more. I gave it away with an old computer (a CP/M machine). One question: where are you getting ribbons for that thing? (Or are you re-inking?)
as has set you on the right track - the NX will emulate a Proprinter II nicely, and all that remains is getting the interface bits figured out. USB-to-serial (or parallel if it's like the one I had) can be tricky. Black Box makes some nice interfacing widgets that work well, but are expensive. I remember they had a parallel over Ethernet printer server in a dongle that was the bomb.
Hope you get those printers going all right. Dot-matrix is noisy and kinda slow, but, yeah, it's reliable and cheap. (And it would be cool in a retro sort of way...)