Good News! This applies to X-308 XJR with 6% pulley: Removed (common) Center muffler, inserted MagnaFlow 10790 2.25" X-pipe, ran extensions back to "before the axle" OEM mufflers. They--and rear mufflers and tips--are OEM. Got a nice, low "burble" at idle, VERY slight (barely noticeable) "hum" at 2000 rpm. Otherwise, a little "growl" on acceleration, but not significant. Just enough to "match" XJR performance and handling. (Jag should have designed a performance exhaust to with XJR package, but I gather "grace" won out over "growl.") I now have an OEM Center muffler and Mina rear exhaust if anyone is interested.

Ed
Aiken, SC