Hi Gomo,
AFAIK Encore doesn't accept single frame MPEG files as source for a still menu. If it did, that would have been the best solution; both the video and the still menu background could have been encoded with ProCoder.
The only route that I can think up at the moment is to create a couple of still menus in a dummy project in Encore, build a Video_TS folder, extract the single frame MPEGs from the VOB and then play around with every setting you can find in ProCoder until you get as close as possible to the "look" of the Encore encoding and finally use those settings for the actual video.
Especially if you are on NTSC (I am a PAL person) the "601" setting could be important. Also see this thread on the Canopus ProCoder forum:
Color space conversion
