Looking at your diagram again, it appears that it would be no different than replacing your X-pipe with a Y and having a SI/DO. The two pipes between the X and the first Y will basically be the same. At least that's the way it seems to me

 

Right that's what I was saying before but I don't think he wants to buy a SI/DO muffler

 

So I've decided I'm gonna do this set up and try something different no ones done it so I guess I'll be the first it's still gonna be way better than a stock set up might not get to for a week or two but I'll post a video showing what it looks like underneath and the sound of it....I like to think up different stuff I had a true dual system on a lifted 95 chev with a di/do muffler ended up breaking one tail pipe off so I got a pre bent 4" pipe for a diesel slip on installed a y on the d/o end of my muffler into the 4" pipe and a 6" tip it sounded pretty good and it was different it was a short box regular cab and I'd get ppl coming up and saying you got a diesel in that thing? Lol anyways that's what these forums are for swapping ideas and trying new stuff

 

Cool! Have fun with it! I hope you get the sound you want without hurting performance! Good luck!