Hard to tell without actual stocking numbers and knowing your water change schedule (both amount changed and how often) on whether the smell is overstocking, trapped debris in the substrate, a bit of both, or something else entirely. Is this a tank with live plants or fake?
While it's impossible to over filter, it is possible to over circulate. My only concern with adding filtration is that your Angels may have trouble with the added current caused by another filter. Their bodies aren't suited for turbulent or fast moving water.
In answer to your original question though, yes, you can add purigen to your canister so long as it's in a bag. You would want to put it where the chemical filtration stage would go. Most people have their canisters set up so that the water goes past mechanical (sponges usually) filtration, then bio filtration (ceramic tubes, bio balls, etc), and then either chemical (carbon, purigen, nitrazorb, etc) or filter floss (for polishing). Most people seem to be going the filter floss route instead of chemical (except for when cleaning out medications after a round of treatment), but it's up to personal preference and budget.
As stated above, Purigen would only mask your underlying problem though.
