ok ive done this twice
1st i did my 3.0 tdi A6 just had POWERFLOW remove the back silencers and replace with stainless pipe and nice tail pipes (it was a tiny bit louder)
2nd i went to powerflow with my 2008 3.0 tdi A8 sport
i told them i wanted it louder so,,
they made a full system cat-back with larger pipe than the standard audi pipes
then added huge tail pipes ...........
it sounded amazing !! not too loud either,,just right,,
So i think a V8 diesel will sound amazing if you do the same....
and only around £400
made to measure there and then while you wait
lifetime warranty too