Sort of sounds like a short cut to a defect notice. The RS6 with the turbos dampening the sound is really on or over the limit with a 3 inch miltek exhaust with no centre mufflers / resonators, when on full song.
NA car will be louder. Rip out the centre mufflers and try it first. It will be just as easy to reverse as your thoughts about the main mufflers. Having an Audi is about class sound, it can be loud at the right time but I really think the rear muffler thing would sound like the exhaust had fallen off.
C5 RS6: Sportec, Milltek & Wagner -- B5 RS4 : modified -- B5 Audi 1.8 quattro 132 Kw -- 2007 VW Touareg TDI 3.0 with air suspension and lockers-- UNIMOG 404 TLF8