I find this grounding scheme very good and acceptable. Noise/RFI/fizz/fuzz/crackle/pop/hum are very minimally heard even at +72dB gain setting.
How it's done:
Basically, both XLR jacks are mounted securely on the metal/aluminum case. Then, pin 1 on each XLR jack (input and output) is also connected to the ground terminal of the XLR jack. Since the metal Neutrik jack is conductive, this also grounds the case.
Both the input and output XLR ground/pin 1 wires are then connected to each other.
Pin 1,2,3 of the XLR jacks are connected to the SC-1 PCB.
You may also lay flat the grounding wire against the back panel and secure it there with a tape.
My test setup:
The outputs of the SC-1 is connected directly to the XLR inputs of a KRK RP-8 monitor so I can hear the noise. Monitor set at normal volume default.
Noise was tested using the scenarios outlined below. This configuration results in the minimal amount of noise for all scenarios listed.