I have made some progress after my installer came round to fix the remote.
My understanding is that the MC "ten foot interface" (Theatre View) is basically a five button interface;
Left, Right, Up, Down, and OK.
Just about all functions are available through those buttons. When you press Up (Down works as well) to see the Subtitles options, keeping pressing Up to scroll through all the options: Volume, Progress Bar, Aspect ratio, Zoom, etc. What displays is dependent on media is being played.
OK, plays and pauses video. Left and Right skip forward and backward in a video, or move around menus.
Lots of other buttons on my Logitech using MCE commands, and on my standard MCE remote also work. Stop, Play, Pause, Record, Back, all the Number Key (which also act as Character Keys in certain areas), Guide Exit, Menu, Info, Clear (acts as Escape), E (Enter). *, #, Channel Up/Down, Volume Up/Down, Mute. Fast Forward and Rewind move back and forward in a video, but it is just skipping through the file, not playing smoothly.
None of those commands have to be learned. They are already defined when you select the Microsoft MCE Remote in MC. If some aren't working for you, have you already learned some value against the command that may be causing a problem? May you should set the Command list to default and see if the other buttons start working.
The learning function is still a bit of a mystery to me. It only seems to learn commands that it already knows about, allowing you to move commands from button to button, but not add new ones. Except when adding an IR Blast command to a function, when it learns any code. I think. I don't use IR Blast functions.
I haven't found a list of MCE codes that MC uses, but the list of commands it uses is shown in the Options > Remote Control > Commands section. Again, you may need to click the "Restore Default List" button to see them all.