I looked at all the manuals on-line. I own the XR45.
XR10 shows a freq response of 10Hz-44kHz + or - 3db and THD 0.9%
XR45 shows a freq response of 10Hz-44kHz + or - 3db and THD 0.3%
XR50 shows a freq response of 10Hz-88kHz + or - 3db and THD 0.09%
Did the TI chips change? Why the differences? The big question I want to know is does each generation sound better? Do the analog ins sound better? Is the difference in the TI chip or in the implementation? Based on an unnamed "engineer at Panasonic", the quality is going down, not up. It is interesting to see how these digital amps evolve.
Digital inputs S/N is 90db for the XR10 and 85db for the XR45 and XR50.
XR10 has no digital output; XR45 and XR50 have one optical out.
Frankly, the XR50 has the same connection setup as the XR45 except it has 2 coax in and 2 optical in, where the XR45 has 1 coax in and 3 optical in.
The tuner and tone controls appear to be the same for all the units. I read somewhere, and I recall it as a reliable (not just a poster) source, that a 100Hz rolloff for the speakers to the sub is a good place to do it, since a 6db/octave slope means you'll be down about the right amount on a typical speaker that goes to 50Hz -3 anyway, so the crossover does not seem to be an issue to me. I haven't seen any feedback that there is trouble integrating a sub with these receivers.
This makes me think the XR50 is the replacement for the XR45, since its weight is also the same. Perhaps the XR30 replaces the XR25. The XR70 is just an XR50 with HDMI and DPLIIx, maybe?
Ben