Gammajo (and others)
The lid I created is 3/4" thick gloss black, acrylic.
I routed a step along the underside perimeter, so it (sits in) the top of the preamp with no screw holes.
The weight alone is plenty for safety reasons or whatever (yeah, I have a cat)
I lined the underside lip with adhesive-back felt strips, for a cushion between it and the top edge of the chassis.
Gaps were left between the strip ends for ventilation purposes, the preamp only gets luke warm, nothing to be concerned about here.
Personally, I think it looks so good, I wouldn't mind manufacturing a few one-offs or supplying dimensions for interested DIY-ers.
My supplier is a local plastic and fabricator shop, they roughed out the initial cut, I finished it.
It took *many-after-work-hours* on the Bridgeport, cutting, shaving and fine tuning for a perfect fit.
It's very hard to upload a good picture (since it's black) but in person, it looks beautiful.