Jones Maxflow - Not great?

Not having tailpipes could absolutly be part of the problem,partialy due to the pulses in the actual tubing and mufflers but also from the soundwaves bouncing under the car,especialy considering how much volume the car body has behind the rearseat that can amplify a reasonance tone so to speak.
Worked with exhaustsystems for over 10 years and its realy hard to predict what works and what doesnt especialy as you go for larger tubing and alitle louder mufflers.