pixinsight is pretty agnostic as far as this goes, it can be used to process any kind of image.
since the duo-band filter passes Ha and OIII, the red channel of your camera will contain the Ha signal and the blue and green channels will contain the OIII signal. so without doing anything your RGB images are pretty much HOO narrowband images to start with. there probably would not be a huge benefit to splitting the channels out and recombining them if you were going to do HOO mappings on that data anyway.
if you want to make an SHO image from data from both filters, then it probably makes sense to split the duo-band data so you can reassemble it with the SII data to make the SHO mapping. in this case when you have your master images from the duo filter, just use ChannelExtraction to get the R, G and B channels from that RGB image. then you'll probably want to merge the G and B images together. there are a lot of ways to do this; you can use PixelMath to add them together, or save them to disk and add each G and B image twice to ImageIntegration and run that with defaults to get the combined B/G master image.
rob
