The manual indeed mentions PC controls, but there are no further details anywhere in the document.
Computer control
The DX-SR8 can be controlled by a personal computer through the serial interface.
Settings of frequency, mode, power, and memory channel can be controlled.
(Optional PC interface cable required)
This video shows that the serial port is available in the cable from the body to head unit and also mentions serial port settings. No word on that being available on the mic connector:
With audio also on RJ-45 is probably possible to use Digirig as the complete replacement of the head unit while operating digital or use both control options with a “Y” splitter or RJ-45. We can look into pinouts if this is something you want to attempt.
Another post where the cable for this radio is discussed (audio/PTT only).