Re: getting any adjustable, 4-spike device perfectly level is tough. I'd try to lean the speaker so three points are touching, then rotate the 4th until it makes solid contact with the floor. Cinch extra nut and you should be there.
Otherwise, very thin shims should be able to do the trick.
Bartok, if you're not going to follow your promised, self-imposed banishment at least stay out of the Zu threads. You don't see us wading into your shallow waters regarding your chosen flavor, hmmm?