I haven't been a visual observer for some years, the site below maybe useful for you. I tried many different filters for galaxies without any success but that was 5 or more years ago. Since galaxies are across a wide spectrum it will be interesting to see if any filter can indeed do anything to enhance them. The cure? A dark sky or make the switch to the dark current as I did.
http://www.spacekb.com/Uwe/Forum.asp...yone-used-them
PeterM.