the Helius Omega and Aurora have a larger pillar so the hole in the armboard needs to be larger. As for the geometry, it depends on whether you get a 9 or 10 inch arm. My Omega is 9" and my Aurora is 10" with replaceable headshells. but I havent found anthing unusual about mounting either. I think the Ruby is a great arm, especially for the price. the 4 ball pivot just makes sense, and is very stable but with little friction.