I think running your Zoom 505II with your Vox is resulting in a "double digital whammy" with the Vox. Putting a digitally-reproduced signal on top of a digitally-reproduced signal often times causes one or the other to get "fussy".
Granted, those are laymen's terms, but when I run my own Zoom G2 pedal through my Valve Jr., or my Classic 30 (both tube amps), the tonal results are positively excellent. I haven't tried the G2 with my Cyber Twin, which is hybrid amp much like the Vox, but probably won't, either, because the tones and effects it has are equal, or superior to the Zoom's. Still, the G2 is a very versatile pedal, and for less than $100 bones, it does a ton of things very well. Haven't had the opportunity to try it with a solid-state amp as of yet. Which speaking of, maybe I need to buy one . . . ?