"The presence speakers only work with the Yamaha DSP modes, but you don't need the presence speakers for the yamaha dsp's to work correctly. If you use the presence speakers, then you can't use the surround back speakers at the same time, it's either one or the other. But I've heard many say that they like the presence speakers better than the surround back."
To clarify the above comment; The presence speakers cut out the 2 extra rear surround speakers for a 7.1 setup, but you can still have a traditional 5.1 setup when using the 2 presence speakers up front. The presence speakers got a favorable review in one of the Audioholic Yamaha A/V Receiver reviews, which prompted me to try them out. It seems to me that they broaden the front sound stage, picking up sound reflected off of the front walls of the room DSP venue selected.
I use wall-mounted (6 ft high) Klipsch 5.1 speakers with a 4" woofer and dual tractix 90 degee side horns that provide 180 degrees sound dispersion. I think this provides an even wider soundstage to all seating positions in the room. They are direct firing in 180 degrees so they are not like dipole or bipole surrounds in that they do not add time delay or phase differences to the already DSP processed sound. I also use these same speakers for the rear surround speakers as these are also fed DSP processed sound which includes direct and indirect spacial signals. These particular speakers are out-of-production but Klipsch makes more expensive successors. With these speakers and a Yamaha HTR-5890 receiver, I am satisfied with the DSP effects.