They all can power those speakers but how well each AVR will perform with them will depend a lot on:
1) seating distance
2) your listening habit, such as how long you listen to
For example, if you sit 4 meters vs 2 meters from the speakers, you will need roughly 4 times the output from the AVR than what you would need if you sit 2 meters from them.
If you listen to reference level (cinema loud), versus say 10 dB lower (still very loud for a lot of people) below reference, then you will need 10 times the output from your AVR.
For those so called 4 ohm nominal speakers, if you want to play safe without considering what your actual requirements are, then go with any of the X4800H, Cinema 40, X6800H, Cinema 30 but add external amps that are rated 200 W 8 ohms, 300 W 4 ohms.
From "power" output stand point, if you are going to use power amps, even the X3800H or the Cinema 50 will still be adequate.
The Denon versus Marantz topic seems popular on forums but in reality the difference is just aesthetic so highly subjective by nature. Other than that, some people believe Marantz use their so called "Soundmaster" to tune their devices to sound warm and musical, but there is no scientific basis, but mostly something created by some very smart marketing people.
People who are subjective oriented, don't understand too much about the underlying science and bench test measurements will tend to buy in to such smart marketing talks, as they are good at providing a lot seemingly good reasons for why Marantz has that "signature" warm and musical sound. My suggestion is, if you can get the Cinema 30 for just a few hundred dollars, such as up to $400, and you like the better look, and perceived better build quality, then go for it, if more than say $500, and the X6800H looks fine to you, then save the money for something that actually matter, but again, that's just my opinion.
