I just got the 4520 today. After running Audyssey, my Ipod n HD Radio freakin rocks. Blu-ray n movies saved on cable, not as dynamic. It would be nice if you could change the speaker DB settings somewhere else instead of the test-tone in audio section of the GUI. I need to make sound adjustments on the fly as Blu-ray movies, hi-def cable movies, sports on cable, and Ipod, all vary in their degree of sound quality. If I have to go into the audio section every time I want to make an adjustment, that's not gonna work for me. The 3100 had five X's as many options in the setup menus allowing you to really tinker with the sound. The options button allowed you to change the speaker db levels, and a few other sound settings. It would, also, save the adjustments I made for each source I was using. I'm downloading the firmware update as we speak. I hope it adds some of the features that are on the 3100 n missing on this one.
I know there's a beast in here, just need to figure out how to unleash it!