just bought a heritage softail and the silencers are far too effective. I want a sound that is very deep but not too loud. Any ideas ?

 

Welcome to the board. Best bet is to go to a local bike hang out or dealer and listen to the bikes that roll in. Talk to people about their pipe/muffler set up and what they like or dislike about it. I purchased a set of SEII slip on mufflers for my softail and have been very happy with them. Sound cruising is rather mild, but when you rap on the throttle they let out a nice bark.
Sounds like HD discontinued the SEII mufflers, though some dealers still have some to sell. Cycle shack makes a slip on muffler for the softail that is less expensive than the SEII with similar sound and performance.
If you change the pipes or mufflers, I highly recommend installing high flow air cleaner and remaping the fuel injection.