@dramatictenor -- congratulations! I, too, compared the 590AXII to the 509 and several other amps before settling on the 590, and reached the same conclusions as yours. Both amps are fairly neutral, but the 590 sprinkles just the right proportions of warmth and palpability to make it a phenomenal component. I have now tried the amp with 4 different pairs of speakers and it has breathed life into each one of them. The loudness option is another cool feature that I use often when listening late in the night.
Enjoy the music!
Enjoy the music!