Two things - the 750 has the video upconversion. It doesn't make your s-video look any better, but it certainly eases the convenience factor, requiring only one connection to the tv from the receiver. It's not like a line doubler on an HDTV that will give you 720p upconversion.
About the "dialogue lift" feature. This is not done with equalization or other acoustical magic tricks. Rather, Yamaha is a proponent of "presence" speakers, which are placed above and behind the front speakers, giving the front soundstage more depth and more airiness. I tried it for a bit, but found the speakers were ugly to look at and that it muddied the sound, rather than making the soundfield more dense. Dialogue lift is done by placing some of the dialogue normally contained in the front soundstage and actually "lifting" it up into the presence speakers. Then, the dialouge actually comes from a point higher in the front soundfield. I don't know if I fully understand why you'd want to do this, but, go figure... It's not, though, a DSP that makes the center channel louder, or produces a "bump" in the voice frequencies.
