I thought that I remembered reading here that the Knight's Armament "QD" Muzzle Compensator that works with the Knight's sound suppressor could bring a 14.5" barrel up to 16" when permenantly attached.  Is this correct?

No it wont, its too short.  AAC makes one that does though.  Do you have a KAC suppressor?  Its a spend A2 flash hider if all you want is the extra length.  Better mounts for suppressors for perm install out there too as the KAC is not a good deal as far as flash suppressors go, nor a first chioce for sound suppressors.  You can use the RD Systems mount behind a Phantom or Vortex, AAC is releasing a Vortex to mount the M4-2000, there is the Bilock for the M4 96D, YHM has a new mount based off the Phantom, etc. all of which reach 14.5" and allow mounting of a suppressor.

Gemtech makes one too called bi-lock.  It doesn't suppress flash as well as a Vortex or Phantom though.

Does RD systems have a website? I googled them but got nothing.

Quoted: Does RD systems have a website? I googled them but got nothing.

They do have a website somewhere.

But they don't make a muzzle device.  They just make a collar that fits over most current muzzle devices (A1, A2, Phantom, Vortex).

http://www.easymation.com/

After going into the ammunition part you should see a section of mil/le products where it shows the Troy suppressors but not a good view of the mounts.  Do a search in the EE for RD Suppressors and Denny has an ad with great pics.

Seberger has sued Troy so RD Systems labels the suppressors RD and not Troy anymore.

Here

RD Suppressor ad