Denon or Yamaha

Neither, Look into Pioneer "Elite" or Sony ES receivers.

How are they better?

Look into the Onyko TX NR809. Good value for power and features.

Didn't say they were better.

Cannot comment on the Denon or Yamaha. That is why I recommended something I have experience with. I owned the Pioneer Elite VSX-29tx, VSX-39tx and the VSX-59txi, also several Sony ES receivers. I compared them at the time with offerings from Yamaha, Denon, Marantz and Integra Research. Based upon my comparisons and research I chose Pioneer "Elite" as my favorite time and again for home theater and surround sound receiver duties in a 5.1 and 2.1 set up.

They consistently excelled at Video processing and Music playback. They look great as well and have stellar audio system set-up software and microphone. http://www.pioneerelectronics.com/PUSA/Home/AV-Receivers/Elite+Receivers/VSX-53

Although I am not currently In the market I would not hesitate to look at the current SC or VSX series of receivers from Pioneer 'Elite". Read the reviews and judge for yourself.