Thank you for your kind comments, Jason.
I have very little experience combining Ha and RGB data (have done two images so far). But have tried and experimented with various approaches, including the scripts available in PI (NBRGBCombination and HaRVB-AIP). In both cases (Carina and Prawn), I ended up combining the fully processed non-linear final Ha and RGB images, using for R an expressions of the form:
RHa = R + (Ha - med(Ha))*factor
where the Ha data was apriori linearly scaled to R. I searched for the highest factor that would not clip the data on either end. Similarly, after an CIE Lab decomposition of the new (RHa)GB image, I did
LsynthHa = Lsynth + (Ha-med(Ha))*factor
also prescaling Ha to Lsynth. This approach seems to preserve very well the color and shape of stars, while enhancing the hydrogen areas both in intensity and contrast.
Hope it helps,
Ignacio