Nobody mentioned the Marantz SR8001 has a toroidal transformer vs. the standard-issue power supply unit in the 4306. I don't know if that's what made the difference, but the Marantz had a much easier time providing great dynamics with hard-to-drive speakers.
I performed a direct comparison between the two and the Marantz, subjectively, had a much more dynamic sound. As far as bells and whistles go, I haven't compared the 4306 and the 8001 specifically, since they are in different price ranges where I live.
However, compared with the 3806, the SR8001 was somewhat equal, with some advantages and some drawbacks, the main one being no real way to send DVD-Audio and SACD signals digitally to the 8001, whereas the 3806 has a Denon Link input. You do have to use an expensive Denon DVD player to use that feature.
