I have seen postings on how an expansion chamber can help reduce noise and cool gasses and read many posts here and elsewhere on how the only way to get a quiet, free flowing exhaust is to use a very large box. Assuming you want a pipe that is perhaps 2 - 2 1/2" diameter for a typical engine...

Is there any value in trying something like
http://www.magnaflow.com/products?partNumber=12773
and then putting (welding) a perforated stainless pipe down the middle of the desired diameter?
you would get a considerable empty volume around the inner perforated pipe and you would also have a large volume of acoustic material. Perhaps the material might last a bit longer being protected by some air gap and an additional perforated pipe.
Or is it a daft idea...?

I made up my own exhaust system with a 400 cell CAT welded in before a stainless 24" x 6" stainless silencer with 2" pipe in and out. Silencer came from http://www.mijexhaust.com/ who sell universal silencers through ebay. It cost about £50.
The car sounds very good with a deep note to the exhaust but is very quiet indeed. I didn't want a lot of noise as it gets to you on a long journey. I suppose my set up is similar to what you propose with the CAT being an expansion chamber then the straight through silencer so I can confirm the idea works.

2.0L Blacktop - just put a 2" bore 5"x 24" from MJ Exhausts - drove it round the block - its so quiet..
Someone said longer silencers are more effective than fat ones ... don't quote me lol