Dual holes through the cover of a Lian Li. I will post pictures later.
Your Lian Li is aluminum, no? If so, then that is the reason why you only used one wheel. Aluminum is MUCH softer than steel.
My recommendation is to draw yourself a chalk circle where you want the hole, and drill a series of holes (3/8" would suffice) around the inside of the hole. Then get yourself a grinding wheel for your dremel (most dremel kits come with this). Note: I do not mean the sanding drum. Use the grinding wheel to get the edges close. Finish with a fine, round file.
Or, if you can stomach the cost -- buy a hole saw. Don't cheap out on the hole saw, you'll regret it.
To protect the case from accidental scratched while handling and working on it, consider covering it with tape in the area you'll be handling and working on - leave the actual pilot hole and area being cut free, so it doesn't catch or gum up the cutters.
Then you can remove it and clean any residual adhesive off.