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Hello ToddI
Yes you can use a Harmony Remote to have more than 6 keys.
In Logitech Database, there is a device name "Plex Player" (Multimedia computer/Plex) which was defined to control Plex. You can use this device to setup your Remote then have it known to Remote Buddy.
That's what i am doing on my MacMini HTPC (still work in progress). If you go to hardware tab in RB preference window, you have to check "enable support for multiple ..." then "Automatically authorize..". From the harmony remote just press a key and RB will discover ids (a number from 150 to 160).
To help identify which keys are corresponding to each remote, you may have to name Remotes to something meaningfull. Here is a list I grab from Plex forum :
Harmony button - RemoteID + Button
OK - 150 Play/Pause
Up - 150 Plus
Down - 150 Minus
Left - 150 Left
Right - 150 Right
VolUp - 152 Plus
VolDn - 152 Minus
ChUp - 158 Plus
ChDown - 158 Minus
Mute - 152 Play/Pause
Prev - 153 Minus
Menu - 150 Menu
Exit - 155 Plus
Guide - 157 Play
Info - 153 Plus
Stop - 151 Play
Replay - 160 Plus
Skip - 160 Minus
Play - 151 Menu
Rec - 155 Minus
Rew - 154 Plus
Fwd -154 Minus
Pause - 152 Menu
1 - 151 Plus
2 - 151 Minus
3 - 151 Left
4 - 151 Right
5 - 152 Left
6 - 152 Right
7 - 153 Left
8 - 153 Right
9 - 154 Left
0 - 154 Right
Clear - 154 Play
Enter - 153 Menu
Blue - 159 Menu
Red - 159 Left
Green - 159 Right
Yellow - 159 Play
Aspect - 157 Plus
LargeUp - 159 Plus
LargeDown - 159 Minus
PwrToggle - 157 Menu
Queue - 157 Minus
Sleep - 154 Menu
F1 - 155 Left
F2 - 155 Right
F3 - 155 Play
F4 - 155 Menu
F5 - 160 Left
F6 - 160 Right
F7 - 160 Play
F8 - 160 Menu
F9 - 158 Left
F10 - 158 Right
F11 - 158 Play
F12 - 158 Menu
F13 - 157 Left
F14 - 157 Right
Regards
Patrick.