I've tried the 580 (twice), 650 (twice), 600, and 800. Over time, I got rid of each. I think the 600 was my favorite of the cheaper series, and the 800 was very nice driven by a DNA Sonett balanced out, but the Stax Lambda Pro/SRM-T1W combo still was better to me; so that went too. Now with the 007's and Spritzer-modded 727A, there's no comparison....
Oddly enough, perhaps my favorite synergy for just pure fun was the 580 with the Eddie Current Lunchbox amp. I listened to that combo a LOT, for decent stretches at a time.