If it was me, rather than get bogged down with every possible code and combination of codes available, I would work out what I want the HTPC and XBMC to do, design a few screens, learn those few codes and start from there.
I looked at all that stuff too regarding XBMC and it really became mind boggling - what made it easier for me was to work out what functionality I wanted - rather than think "oooh look, I can do all that!". You make the technology do what you need rather than what others wanted on their HTPCs. Then as you become more aware of what you can do with the XBMC you can then begin to update your configuration and learn more codes and use more functions.
I'm running XBMC on my first gen AppleTV (ATV1) and I use the standard ATV remote codes which do everything I need at the moment. That is literallly 6 buttons!
Out of the "trillions" of functions you say there are on XBMC HTPC combination, you are unlikely to use that many.
RC9500, RC5400, RU940 & Pronto Neo, Windows Vista.
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