obet: i think i can spare you a couple of those hairy things!
hehehe. I'll let you know if they're ready.
As to overflow designs for your nano cube, maybe you can check this out:
http://www.zeroedgeaquarium.com/FAQ.htm
You can make your backwall as your overflow and incorporate a small box under the base of the tank that contains a sponge.This will minimize a lot of noise.However, cutting a square or rectangular hole in the base would be something i can't decipher. Maybe mang Ramon can do it. Also you have to design the cabinet to accomodate the box.
Since you want to drill the base of the tank to hide the return pipe, either you still have to raise the output high enough or put a check valve( if you can find a good and reliable one that is saltwater safe).
http://www.zeroedgeaquarium.com/Plumbingdiagram.jpg.jpg
As for my zero-edge drain, i simply drilled four holes(two on each side) in the canal(overflow) and simply glued some airline hoses to the lip of the canal and the other end is just about an inch into the drain hole and it reduced the sound a great deal.
I would not recommend this for a bedroom tank but for a living room tank, i would say that the sound it produces is more soothing, like a waterfall effect and very relaxing.
Good luck with your new quest