buckswope's got it covered, but let me see if I can explain myself better. You can have 24 devices in an MX-810 and they can be anywhere in the house (using RF to control components in a cabinet or another room). An activity macro (ie: "Watch TV" or "Listen to Music") can be programed using any of these devices. If you want to watch TV or listen to music in another room, you would set up another activity macro for that use (ie: Watch TV 2). This is the same way the Harmony remotes are setup.
With the MX-900, you have "Watch" and "Listen" main pages, so you could have "Watch" TV-BR, TV-LR etc. Or, you could just have links to go to another Watch page with all the activities for a specific room. For example, on the 1st Watch page, you could have a button labeled "BEDROOM". Pushing it would take you to another Watch page with TV, DVD etc.
Surf Remote Control