My bet would be that the problem you’re having is with the storage being remote, and not with the PC. As long as you’re running Roon Core (so the server part) on your PC, and not on the NAS, the amount of RAM on the NAS should be irrelevant, because “all” it is doing is serving the files to your PC, and not doing any of the heavy lifting that Roon requires ressources for.
Attaching an SSD to the NAS server is probably useless unless it is powerful enough to run Roon Core (if you’re running a DS 18xx, so the one with an intel processor, it might be OK depending on the number of tracks, but my assumption is that given how much volume of data you have, you’d already be pushing it, so that’s probably not what you want to do).
The way I see it, what you want is to directly attach your storage to the machine running your roon server (or “core”) - think “big USB drive”, there are 16TB single drives at this point after all, and back that up elsewhere (like on your NAS, which you would then use as it was intended to be). This can either be your current computer, or, if you choose to go all-in with Roon, either a NUC running just Roon (in which case you’d definitely want an i7 nuc given how many tracks we’re likely talking about).
In any case, please follow @wizardofoz’s advice and fill in the details of your setup, including how everything is networked (i.e, is it hardwired, or over wifi ?) and the number of endpoints (so playback zones).