"-Some people are saying the SA-XR50 is the replacement for the SA-XR45 and the SA-XR70 is completely new. Does anyone know for sure?-"
Both the XR50 and 70 are new. The 50 replaces the 25 and the 70 replaces the 45.
The design/features of the 50 and 70 have some new things and are mostly similar just like the 25 and 45 are very similar.
The 50/70 seems to have vents on top instead of rear fan, and digital in for DVD-A, but it seems like the overall marketing of these Pannies is to have the cheaper/worse power supply version -the 25 and now 50 being sold in regular stores and the 45/70 to be harder to find or only available online.
I know NO store around here had the 45 (or ever had it in their computers) but the 25 was at Best Buy, Ultimate Electronics, etc...
I dunno why they seem to do it that way, but it seems like that's how they're doing it.
I'd get the 70. Or... wait for someone who gets both and opens them up and posts pics, but I think just getting the 70 is safe bet.