In preparation for the ARRL DX contest, I am setting up for SSB.  I only do this twice a year so it feels like starting over each time.
The setup - I have a Yamaha CM-500 headset.  The headphone plug goes into my RemoteRig client box.  The MIC plug goes into an MFJ-434B Voice Keyer and then on to the RemoteRig box.  On the Radio end, there is a cable from the Remote Rig box to the Flex 6300 microphone jack and one to the headphone jack.
The problem - I get a loud and garbled echo in my headphones of the SSB being sent.  It could be either a canned message from the Voice Keyer or just from the microphone, no difference.
I can get rid of the echo by setting Advanced > RTP tx mode to Normal.  However, I use VOX in a contest So I need RTP tx mode to be set to Continous.  
I tried changing Advanced > Full Duplex to either YES it NO but the problem is still there as long as RTP tx mode is Continous.
I am sure I am missing a parameter but trial and error have only yielded error.
Does anyone know the magic setting?  This worked last year.
73 de K1ESE
John