The 591 is the 1612 which gets you over the 1513
Since when did the 591BA come with the 1612 receiver? It used to come with the AVR 591 receiver which is different from the 1612.
I own the Denon 591 receiver and the differences from the 1513 are all the things mentioned above plus the ability to convert analog video to HDMI which the 1612 nor 1513 do. And it also has a component video input which the 1612 and 1513 do not have.