The Bönez Superflo exhaust on my 90 vert has a 'presilencer' ahead of the cat. I run the Superflow through the 'Y' back to two 22" turbo mufflers I think it sounds fantastic. Deep and mellow. Pretty subdued on the highway.
The presilencer looks for all the world like a glass-pack. I have had 2 different exhaust guys tell me that it is a glass pack. I cut it out when replacing the catalytic converter this summer, but the exhaust sounded harsh and raspy. Inside, it looks like a glasspack. I put it back in and am again satisfied with the sound.
It probably is not a glasspack, it is probably made with stainless steel packing, cause it is not burning out. Rotary Performance should know how to make this work.
When I got the car it had no mufflers, just the Bonez Superflow system. At 3800 rpm, it made my ears bleed. At 8000 rpm, it would make the neighbors' cat sterile.
I think there is a place for this type of muffler as a presilencer in the RX7 exhaust, provided you can get one that will not burn out. Obviously, it will not be a glasspacked muffler but a more durable stainless packed version of the same type.