Background:
The TS-930 has a very high impedance on the microphone line (approximately 100K). When using the DXD with a 930, audio may be coupled from the headphone circuit to the mic input via the capacitance of the cable between the DXD and the 930. This would only happen when the 930 was not the selected radio for TX, and the microphone was disconnected from it. This audio coupling could result in tripping the VOX on the 930.
Modification:
A solution is to shunt the microphone lead to the microphone return line with a 5.1K (non-critical value) resistor. This resistor can be placed at any point in the circuit between the the DXD and the 930. A convenient location is inside the DXD, on the rear of the DIN jack. The photo shows a 5.1K 1/8W carbon resistor soldered between Pins 1 and 7 of J3, which is the jack for Radio 2. The resistor could have been put on J2 (Radio 1), if that was the TS-930.
Thanks to Rick, N6XI for pointing out this situation to us.