RSBs:
RSE never made a mac compatible photoshop plugin for RSB files (the irony.. a photoshop plugin that's pc only), so unfortunately it's impossible to open and resave rsb's on macs. which is a shame, because I'd be playing with kit icons, etc.
AIFFs:
wavs will play properly in mac GR but the sound volume won't scale down with distance. so if you're in hearing range of the weapon being fired it will sound like it's right next to you, unless it's an aiff. also, filenames in effects.xml still have to end in .wav. it makes no sense, I know.
There is no technical reason why either of these problems should ever have been issues; blame it on the poor quality mac porting of GR.
On the other hand, blame .exe's on windows users' installer fetish. Installers and uninstallers are used to properly configure virtually every software program for windows. true drag and drop is unheard of and I certainly don't know of a major app that doesn't use an installer on windows. windows users simply aren't used to placing files where they need to go by hand, because moving things around like that is a big no no (broken dlls). so that's why we mac users are left out in the cold when modders package their mods in .exe installers rather than something cross platform like .sitx, .sit, .Bzip, .Arc, .hqx, .bin, .btoa, .tar, .uu, .uue, .as, .cpt, .pf, .lha, .lzh, .zip, .dd, .GZip, .z, .taz, .enc, .rar....