Yes use your filter as a muffler it will help.
But here is what I did and you might gain some help in your thoughts with your design.
I used 2 pieces of a/c flex duct a 300 inside a 600 as a muffler to duct my exhaust outside and I found most of the noise come straight through the elbow on my system on the outlet of the DC. I added more sound deadening around the outside of the elbow and around the impeller housing to cut the noise down.