I've just looked at the GMMK. It's apparently based on another Chinese keyboard that I also have, modified for hot-swapping. The switch sockets seem to be of the better kind, like on the Zhuque, but the Zhuque case quality seems much higher to me (all-metal vs ABS plastic with metal on the top plate only, with an edge that will get scratched easily).
The GMMK does have RGB backlight though, which the Zhuque does not, as it's a 2015 design. The Kananic L/S 82 has an RGB version as well. The Zhuque's biggest weakness is the garish backlight (different unrelated color for each row). It improves the looks tremendously when you change all the LEDs to white/warm white.
There's the underlying question of the layout as well. I'd recommend going for the standard 87-key TKL over the 82, which isn't really that much smaller but much less comfortable to use (a matter of preference though). You'll also have much more choice of replacement keycaps. On the other hand, the keycaps on the Kananic L/S 82 are one of the nicest things about it, as they're PBT and the typeface is more neutral. The Zhuque keycaps, although not PBT, have a somewhat better feel to them than the standard ABS but you'll likely want to replace them anyway due to the ugly "gamer" typeface (which for some reason appears on most Chinese keyboards).
In any case, I'd advise against using O-rings, as they don't really make things much more silent but ruin the feeling of bottoming-out (again, a matter of preference though). If you decide to go for the O-rings anyway, be aware that with the cheaper key sets you'll likely have to stack multiple rings per keycap (3-4 perhaps, depending on the row).
