Interesting. I was just planning on getting some 590 CR18 rims. Not too many choices in double wall rims in that size. I've been happy with the CR18's I have in the 622 size with regards to tire mounting.
I've read elsewhere that the 584 (650B size) Sun CR18 rims that were on the market a few years ago were notorious for being a tight fit.
I think the biggest problem is that the tolerance stack up for rims and tires sometimes work against each other. Tires and rims have manufacturing tolerances and due to the nature of mass production by various companies I imagine that the tolerance stack for a particular tire/rim combo sometimes makes things very tight fitting. For example, a particular rim is on the big side of the tolerance and the tire is on the small side of the tolerance. Both might be within their respective tolerance, but it makes fitment a real pain.
To the OP, I know that tires aren't cheap, but have you tried any other 590 tires to see if it is the rim or the tire?