Ammm I'm not sure the following helps (as I could find nothing at MS) but I found the following at :
http://www.byremote.com.au/Hip/mce_remote_faq.htm"MCE keyboard shortcuts" "Description Key Hip Command" "(Keystroke or SendMessage Commands)" Move up UP ARROW {UP}
Move down DOWN ARROW {DOWN}
Move left LEFT ARROW {LEFT}
Move right RIGHT ARROW {RIGHT}
Select ENTER or SPACEBAR {ENTER} or {SPACE}
Jump back one page at a time PAGE UP {PGUP}
Jump ahead one page at a time PAGE DOWN {PGDN}
Start Media Center Windows logo key+ALT+ENTER *@{ENTER}
Go back to the previous screen or backspace a single character in Search BACKSPACE {BKSP} or {@793,0,65536}
Toggle full screen mode or window mode ALT+ENTER @{ENTER}
Change channels
Change to a specific channel 0..9 0..9
Move up one channel EQUAL (=) or CTRL+EQUAL = or ^= or {@793,0,3342336}
Move down one channel MINUS (-) or CTRL+MINUS - or ^- or {@793,0,3407872}
Menu shortcuts take you directly to the main menus for feature areas. My TV CTRL+SHIFT+T ^!t
My Music CTRL+M ^m
My Videos CTRL+E ^e
My Pictures CTRL+I ^i
TV and DVD menus Guide CTRL+G ^g
Record CTRL+R ^r or {@793,0,3145728}
Details CTRL+D ^d
DVD Menu CTRL+SHIFT+M ^!m
Recorded TV CTRL+O ^o
DVD Audio CTRL+SHIFT+A ^!a
DVD Subtitle CTRL+U ^u
Transport controls control the playback of your media.Pause CTRL+P ^p or {@793,0,3080192}
Play CTRL+SHIFT+P ^!p or {@793,0,3014656}
Play/Pause {@793,0,917504}
Stop CTRL+SHIFT+S ^!s or {@793,0,851968}
Replay CTRL+B ^b or {@793,0,786432}
Skip CTRL+F ^f or {@793,0,720896}
Rewind CTRL+SHIFT+B ^!b or {@793,0,3276800}
Fast Forward CTRL+SHIFT+F ^!f or {@793,0,3211264}
Mute F8 {F8} or {@793,0,524288}
Volume Down F9 {F9} or {@793,0,589824}
Volume Up F10 {F10} {@793,0,655360}