The 4810 replaced my 4802. At first I was a little disappointed with the weight difference. My old 4802 felt more substantial and with 2 more "channels" I would have thought it would be heavier. Not to worry, the internal amps sound very good.
I only use 4 of the 4810's internal amps and Emotiva amps for the rest of my 11.1/3.
I cannot comment on the 4 ohm speaker capability, but like Seattle, I would be a little leary of using 4 ohm speakers with the 4810 (Emo amps would cure this problem and a great sale going on right now
I WILL say the 4810 is an Excellent Pre/Pro and to me sounds better than the pre amp
that I heard at "Emofest". I have Zero regrets on choosing it over the UMC-1, Onkyo 5507 and the Integra 80.1. I looked at all of these products and spent many hours debating the pros and cons of each....
I have auditioned systems that cost many times more than mine, and although they might have sounded better in some ways, I have yet to hear anyone's system that I like better overall.
When compared to my old 7.1 system that I have had for years;
the 11.1/3 makes a Huge difference in mutichannel stero and a more subtle difference when watching movies (but even with movies the difference is enough to make you smile).
When my wife first heard the new receiver, amps and additional speakers (height and wide), her eyes lit up and she said "WOW"! What more could a man ask for?