I ended up just doing a muffler delete on my 3.7 and I like the way it sounds. It's not too loud but it has a deep growl. There's a slight drone but not too noticeable.
Seems like the 3.7 doesn't get much love with mods lol. What setup did you end up with if you've made a decision. I'm currently in the process of modding my 3.7