Yes, the Omega has mufflers, the Zeta is a muffler delete. I only have the axleback with NGM intakes. The customer had a K&N intake though, so performance-wise aside from Magnaflow catback vs NGM axleback they're basically identical setups.
Omega is extremely quiet. I've got the new version on my car that I've been testing out. It's a bit too quiet though, so we may either continue testing or ditch the project altogether and just do Zeta's. When I had the Zeta on my Stinger, it did have drone (to be expected) but after a week or two it wasn't difficult to adjust how I drove in terms of throttle and also get used to the extra sound. Also we added soundproofing to the trunk and that reduced it immensely.