
Hi Les
I remember reading about your problems with this door on your original (top quality) thread.
You have to remember that sound travels through air and air alone. the semi rated door should well be fine but I think its the frame and surrounding area you need to concentrate on also.
This may sound silly but have you tried taping up the gaps in the door with a non pourous tape and then seeing the difference? draft excluders make a big difference (as long as they fit snug) and I maybe wrong but this could be the answer to sound travel through that area, rather than a full fire door.
The heavier duty door will help but sealing gaps will help far more IMO.
Good luck matey