It really can't be that difficult to sort out this page-down issue, though.... and, hopefully, the jump to letter in the playlist. Otherwise, the IR remote is actually controlling it (UI2) very well for me and it's MUCH easier for my wife and children to work with. Also great having a "button" for pause, stop, mute, etc. Those are things you typically want to do in a hurry so to just pick up the remote and press the button works really well.
The pgup/pgdn issues may be solved fairly easily. If we can determine the exact cause... Are you using a Windows MCE remote?
I'm finding I have to use the "search" facility to get to the performer/title I want but it would be nice to browse. Would also be nice to be able to use the "first letter" jump-to list which also doesn't seem possible with a basic IR remote.
Making the letters accessible to an IR remote will take a bunch of grunt work with HADesigner. Not an easy task but, as far as I know, it could be done. HADesigner is a real beast and very un-friendly to use. tschak may be able to provide a little more insight into what would be required to activate these buttons for non-mouse selection.