mpeach:
Sorry but I don't know if moving the mufflers upstream would deepen the tone. It's a question for somebody who has done it or an acoustical engineer. Doesn't
Pypes offer some round race mufflers that are upstream of the axle?
On my old '98, the mufflers were under the seats and the cabin would bet pretty boomy (resonance/drone) at 1800 to 2000 rpm but it was tolerable. I suspect that Ford moved the mufflers to keep the cabin quiet.
sierralx:
Borla Atak axle-back is very aggressive but droneless.
Corsa Extremes, too. I have never heard the Hearthrob mufflers but you could run a search (here and on other forums) for 'drone+hearthrob' and see if anything shows up.
Chris