thanks guys.
i went back and had another go. i already had some HA as red in a lighten layer etc but played with Greg's tips for awhile. in the end the thing that helped the most was increasing the contrast on my RGB data. i've also got my star colours back.. hadn't noticed how much i screwed them up in my haste last time. have updated the file at same link as before:
http://philhart.com/gallery/Astropho...geViewsIndex=1
i'm much happier with this version..
Phil