Chris, in perusing Yamaha's web site, it appears that the 'C920 is the same player as the 'C6480. The only difference is that the 'C6480 is included in a home-theater-in-a-box system as well as being available alone, while the 'C920 is only available alone. There have been some discussions about the 'C920/'C6480 here. A search should prove helpful. This player looks to be a good value at around $400.
Matt, you may have noticed that Yamaha DVD players get little attention here in general. The top-of-the-line 'CX1 has been discussed here only a few times, while comparably priced players like the Sony 'S9000ES and Denon '3800 have been discussed ad nauseum.
Chris, good question. Last time I checked, these models were still up on Yamaha's web site, but dealers have been discounting them. A few weeks ago, OneCall was blowing out the 'C6480 (equivalent to the 'C920) for $359.10. In any event, I have not heard of any replacement DVD-Audio players coming down the pike. Yamaha will be releasing the 'S2300 single-disc universal player (DVD-Audio and SACD) soon, so perhaps they will be focusing their efforts on universal models from here on out.
Chris, Panasonic players have a great reputation on the video side, as they don't show the chroma bug. I don't know how the Yamaha changers compare in this area. However, I doubt the Panasonic 'CP72 will keep up with the Yamaha models on the audio side. For one thing, the 'CP72 is much cheaper. Also, in my experience, Panasonic players are O.K. with audio, but not great. I feel Yamaha makes better audio components in general. Just my opinion. All of this said, I have a Technics DVD-Audio player (part of Matsushita, like Panasonic), and it is a good DVD-Audio player. With CDs, it is lackluster, though.
Chris, I haven't heard of that one. Does the brochure you have list retail prices? I can tell you that the 'S830 will be a single-disc player. The 'S' in the model number is the dead giveaway there. Yamaha uses a 'C' or 'CX' to denote changers.
I bought the CX1 about 2 weeks ago and am very pleased so far with it's performance. Ergonomically I am slightly less impressed with the remote and how the menus are laid out. Not as easy to operate as my Sony DVPS-7700. For what I paid and what it can do I am happy. I almost bought the 920 but the CX1 was only $100 more.