Did you do traditional prep?
Some people use ginger beer/ginger ale/anything ginger and claim that it helps. Doesn't really help me.
Doubling up on strainers is another method, but I would think that would weaken effects. I haven't tried it for that reason. I don't think there really is a way to avoid stomach issues/nausea with traditional prep because of the consistency of the root fibers and taste.

Extracts are probably the only way to avoid it but like I said in my previous post, I wouldn't trust alcohol/ethanol based extracts. See this post How long does Kava take to Extract ?

I did try out Kalm with Kava's concentrate again, but it didn't really do all that much other than a little sedation.
That might just be me though. I don't know. No nausea though, at least.