I installed Screaming Eagle Slip-on's on my 08 FLSTC and I have to say they are way louder and have a deep rumble to them as well. I had bought them 3rd hand, and I guess the other two thought they were too quite, but I think they are perfect. One man's idea of loud is another man's quite.
The mufflers I bought are Slash Downs PT# 64900-99 and retail for $319.00 from Harley. Like I said I am the 3rd owner and my cost was $75.00.
If you want something louder and deeper but not so loud your neighbors all would like you to crash on it. This might be the mufflers for you.
David