Getting late into the mix, but it never hurts to add 2 cents for later readers.
I own a pair of the Dali 800s, and to be honest I listened to it a few years ago with a Macintosh tube amp, and it simply didn't have the stones to bring out the firm mids and lows that these speakers can reproduce. (Note: I also listened to it with a Mac preamp, but the sound wasn't nearly as precise and soundstage wasn't as well defined as a Cary pre and a Modwright pre that I also tested out on the system). However, I wanted to get more warmth into the system, so I opted for a Butler 2250 hybrid amp (solid state guts with the mellowing assistance of tubes) and a Modwright 9.0SWL preamp.
That pairing has worked out very nicely over the last several years (after rolling the tubes in the Modwright and getting their sweetening package) and is so listenable that I sit in front of the stereo for hours on end (which I guess is the ultimate goal and statement about a system). With that said, I'm also getting the itch to try a something a bit different with the amps (maybe some Bel Cantos or NuForce monoblocks) just to see how they drive the Dalis.
I noticed that some people in the forums here have mentioned that the 800s sound better in a larger room and the 400s in a smaller, but I don't agree. I've had the 800s in both small and large rooms, and I've noticed very little difference (maybe, maybe a slightly tighter soundstage in a smaller room, but that's pushing it). It's all about playing with the right positioning and putting in the right treatments (which, admittedly, took me a good 6 months until I was happy in either room).