Charles & Sandra Cohen
I can tell you how it works on the IC-706, and I'll bet it's the same on the IC-7000:
. . . The signal for VOX activation is derived from the output of the microphone preamp.
. . . You _cannot_ use VOX if the audio input comes from the DATA jack,
. . . since that signal doesn't run through the mic preamp.
My _guess_ is that , if you use CAT commands to go from RX to TX, the input from the DATA jack _will_ be picked up, and used for audio drive.
By design, you are _supposed_ to use the PTT line on the DATA jack itself, when using audio input from the DATA jack.
FWIW (you didn't ask this question):
Over several years of watching "digital mode" forums, I've noticed that the interface that's most likely to work, trouble-free, is the Tigertronics SignaLink USB. That just does audio in/out (to the computer) and PTT (to the rig). It doesn't handle CAT commands, or "true RTTY", or on/off CW..
. Charles / VA7CPC