Since I will use many sounds and music in my map, I will need to compress everything as good as I can.

Atm I'm using Audacity and export sounds at 0 quality that compresses the files pretty well.

But I've noticed that the files become even smaller if I iterate the exporting.

So is there a program that can compress an ogg even better or are there some tweaks I can make to cut the file size?

All sounds are mono and should be in low quality already (origins are pretty old wav files [Diablo 1]), so I guess that it might be possible to compress further...