I use the 590s as mains, 580s as surrounds. I've not tried the 580s as mains as I had the 590s first. I'd agree they're fairly similar, altho the 590 is just a bit more capable and a bit higher sensitivity, altho the 590 physically is significantly larger, too. I wouldn't use the 590s or 580s without subs, though; they don't dig all that deep (f6 is 35 hz on the 590 vs 40 for the 580). One thing is that at the time I bought my 590s, they were $900/pair delivered while the 580s weren't being discounted at all at $1600/pr....I did eventually pickup the 580s on a sale for $518/pr. These sales come up a few times a year it seems. What is the pricing you're looking at?