Hello, from what I have seen on all of the forums about co2 conversions, they are not good. They are really inconsistent fps wise and tend to leak and bust there seals, regardless of the brand. I did see one lucky guy get it to work quite well with a lot of teflon modding and some type of specialty bucking. If you are having problems with the guns cycle, evike and airsoft Atlanta are slowly getting in new trigger boxes which should solve all of your problems.http://www.evike.com/product_info.php?products_id=41495
Hope this helps, if you have any other problems go ahead and post it!
Oh and as for sound reduction, it would most likely be the same, just in a more of a crack then a pop