There are resonators on ebay for $20-$30 each that should help, even up to a three inch size. A pair of them would be cheaper than new mufflers. Then there is also the $40 muffler test on engine masters, where they did hp and sound tests of three different styles of muffler,,straight thru, chambered and turbo,
Then there is something called the helmholz resonator. It does nothing to interfere with exhaust flow at all, it just eliminates drone. The catch is finding room to make one (there is no such thing as a of-the-shelf part) and calculating the size and length required. It is basically a j-shaped pipe with a cap on the end, cut into the exhaust pipe, kind of like an h pipe would be. The calculations are on the net, just have to google for info.
I'm also using 3 1/2 aero flow hookers on my small block tina, and 3" magna flows on my big block opel. The aeros are more mellow, even without tailpipes, i didn't like the sound as much as the flowmasters at first, but i'm used to it now, and like them much better. The magnaflows are straight thru, but they are huge,,and sound like very,very quiet glasspacks. I think i might put aeros on the opel too.