As A general rule for these analog only projects:
Have only ONE chassis ground point, with a good size, short wire from the power plug ground terminal to a star washered ground lug secured to the chassis (rack box)
From the chassis ground point, run ONE ground wire to the (or each) circuit board (including the power supply board, if there is one)
DO NOT connect any audio I/O cable ground wires to the circuit boards, connect only at the I/O connector, and run a wire from this to the chassis ground point.
If you want to be super flexible, take the audio connector grounds to ground lift switches on their way to the chassis ground.
Think about it....if there are noise currents on the audio ground cables that you are plugging in to your box, do you want them to flow through the entire audio circuit on their way to ground?
Mount the circuit boards with iso washers or plastic stand offs to be sure they do not short to ground.
This is a star ground, and elimanates ground loops
It will work very well on your GSSL
(yes, this has been stated here many times, but I hope it helps & bears repeating)