Some of the older Denons were built on panasonic architechture. The Denon 900 shared alot of technology w/ the Panasonic RP62 while the Denon 1600 shared w/ the Panasonic RP82. The Denon 4800 was also a 5disc player built on the RP91. The 1600 and 4800 both added better DACs and Bass Management for DVD-A. Since then I beleive the technology sharing has stopped, especially since Panasonic went to an in house all-in-one mpeg decode & deinterlacing chip. Panasonic finally came back to the Faroudja deinterlacer w/ the upcomming S97 scaling HDMI player. I don't think it shares any technology w/ the current Denons, but I could be wrong.
But some of the Denon DVD players do share technology with Marantz DVD players. The software might be different but if you lift the hood and look underneath they are almost the same.
Denon DVD-1400 and Marantz DV6400 are examples of this.
But to muddy the waters further, the Marantz 8300 and 8400 were based on the Pioneer DV-47a. I'm not sure if anyone knows yet conclusively what the origins of the new 9500 are.
This is interesting, as I bought the DV6400 because I found it had better audio than the Denon 2200 and almost as good as the 2900. Moreover, here in Canada, the Marantz retails for 400$ and 1000$ less than the respective Denon models (which also aided my decision). The 1400 is not available on this side of the Atlantic, or I'd have considered it.