I tried searching, but I'm getting some conflicting information.

Weapon sounds should be:
System 7 sound, 8-bit, 11.025 kHz.
And this is for Nova or Override? Or can Nova do better?
My sounds at this quality are sounding fairly poor.

Landing sounds can be 22.5 kHz?

Check out the audio guide from the link in my sig. I'm not sure about EV/O but I suspect the only difference will be they probably don't support IMA compression.