As Zzzzzeke mentioned, if you are refering to your GP, you have a different setup as the Bonneville. The F-body/Bonneville muffler (for 1992-1999) is a transversely mounted muffler located just in front of the rear bumper. I doubt if you have the hangers to mount such a muffler.
To answer your question regarding the sound...if you have a cherry bomb and nothing else, it will be louder than if you have a cherry bomb and an additional muffler. The best thing to do is to go to a muffler shop and ask their opinion. They can make a splitter off of one muffler and run it back for you--but be careful what you do. We all need some back pressure or we will loose some of our torque. My suggestion is to ask the professionals. They can tell you all you need to know about performance mufflers and the pros and cons of using a cherry bomb. Cherry bombs were popular in the 1960'*-1970'* when cars were not as technologically advanced. They are still in use today--albeit mostly on older cars. You may wish to gleen the advice of at least two muffler shops, as some of them have contracts with specific manufacturers and will only promote that brand.
Good luck and keep us informed.
Retired Moderator, The Bonneville Club www.bonnevilleclub.com
RIP Oldsmobile, April 29
1995 Bonneville SE Supercharged (Stock)
Current Mods: Dirty GYM Sock air freshener.