I'm not big into ROMplers, but I do use Nexus sometimes as a CPU saving tactic when I need a strong sound but don't have a lot of CPU cycles to spend on it and I'm willing to give up some versatility/programmability.
Along the lines of Proteus, you might try the free Proteus plug-in. I haven't loaded it in many years but last time I did, I felt it was true to the original Proteus.
http://www.creative.com/emu/proteusvx/
As I recall it was one of those freebies that was definitely worth the download.