Ok, here is another possibility to look at if you are having this issue. Make sure that your tentacle sync is set up for “line out.” and not “mic out.” This issue set me back about 3 hours…I took my TRS to LEMO cable apart to verify its wiring, and I checked all kinds of other settings, internet searches, etc…with no luck.
I finally connected some alligator clips directly to the back of the TRS connector while connected to the tentacle sync to some headphones and noticed the volume a little low and BAM it hit me. It was set on “mic out.” So, needless to say the SD633 could not read the signal until I changed it to “line level.” I knew it was supposed to be “line level” but I overlooked it and it cost me some time. Hope this helps.