Actionbar 2 is actually ActionBar
Page 2. It may seem redundant to say this but it's not.
As you've noted, ActionBar Page 3's button 1 can be accessed through 'MultiBarRightButton1'.
This is because MultiBarRight and ActionBarPage3 are the same. Page 4 is MultiBarLeft, page 5 is MultiBarBottomRight and Page 6 is MultiBarBottomLeft.
There is NO independently visible bar for Page 2. Page 2 is the only one of the 5 additional bars that works solely on the main Action Buttons Bar's paging system (which you can changethrough the paging arrows up and down next to the page indicator - or keybinds if set).
What happens when Page 2 (or Page 3, 4, ...) is active is that its buttons replace the buttons on Page 1. So, if this page is active, you would refer Page 2's first button as ActionButton1.
IF Page 2 is active.
Fortunately, there is a macro command to change actionbar pages and said command can be called several times in one single macro. So, to /click the first button on ActionBar Page 2, this macro will work:
Code:
/changeactionbar 2
/click ActionButton1
/changeactionbar 1
Change the /click line to the button number you want and you're set.
As a sidenote, there is an addon that creates a new action bar for page 2. It does not change any of the default ones you can use to put spells on (1, 3, 4, etc) but (to make room for the new bar) does change the MicroMenu and Bags bar to something tucked to the far right of the bottom of the screen. Your default Keybindings menu will also include options to set them for this new bar.
In case you're interested:
http://www.wowinterface.com/download...3830-b2ui.html