The 590AXII is superb. I've been around the block with this hobby, let me tell you, this integrated does everything extremely well. Besides the typical audiophile grade tricks, it manages to be engaging and musical. I have not compared the 509 to 590 but being that I typically do like well executed Class A sound, the 590AXII delivers. Since putting together the Luxman integrated with the Luxman SACD and Harbeth 30.2 speakers, I have no further plans to change any of the components for the next decade at least.