It looks like my options for naming the inputs is pretty limited
actually, as SoM pointed out that is totally false, you can rename your inputs to whatever you want! you even get symbols, upper case vs lower case, etc. See pg 39 of the 2310CI manual. with the ability to reassign inputs you actually have an extremely flexible system; excluding PHONO and TUNER (which can't be used for anything else) there are eight usable input names (seven video inputs + one audio only input) that you can fool around with.
Another question, I have an older Sony Grand Wega 4 (2004) with (as I understand it) a fixed pixel resolution of 768, rather than the standard 720. It looks like the closest I can output from the Denon would be 720p, so just about everything is going to be scaled twice. It's unfortunate because the Denon will probably be better at scaling than the Sony, but it'll still need the 720->768 scaling on the Sony. I'll play with it but does anyone have any thoughts?
again, as SoM correctly points out this is a very common HDTV resolution (my 50" plasma is also 768p) and these sets are designed to look great with 1080i/720p inputs.
I am assuming your set doesn't accept 1080p, and 1080i is the highest resolution it could accept? I would suggest you simply try out 720p vs 1080i as the scaling output resolution and see how things go. In my experience, 768p displays look best when fed the highest resolution possible (1080i) because downscaling is much easier than upscaling.
So I would let any native 720p/1080i sources pass through untouched, and any SD sources (480i/p) you should test the output resolution options and see if you can tell a difference. Again, the Denon is very flexible in this regard as you can set the video processing options separately by input. So, for example, you can have video processing turned off on the Blu Ray player, have the Wii scaled up to 1080i, etc.