Bold narrowband colours Eddie! Actually, I believe you've got sufficient data in SII. The palette simply needs to be managed better. Despite the data being black clipped (loss of details in the shadows), its got a lot going for it, especially the fine details. IMO, I suggest you focus on the processing for a while to get the most from your hard earned data. There are a variety of methods to processing a narrowband image. Here's is a
good thread to get you thinking about your workflow and ways to improve. Clipping masks provide incredible flexibility if you're up to the challenge. Regardless of the image you're processing, always keep a close eye on the histogram throughout the routine. Its a great troubleshooting tool when things go wrong or if you're trying to extract the most from the data. Look forward to seeing how you progress - keep at it!