Auto-Install Software

Give this a go, @noisneil. Long-form and arrow-headed for readability.

It seems the trick is to select the row containing the checkbox before you click the checkbox...

tell application "System Events"
	tell application process "Installer"
		tell window 1
			tell group 1
				tell splitter group 1
					tell group 1
						tell scroll area 1
							tell outline 1
								repeat with eachRow in (get every row)
									set cbName to name of checkbox 1 of eachRow
									if cbName contains "AAX" or cbName contains "VST" then
										select eachRow
										tell checkbox 1 of eachRow
											click
										end tell
									end if
								end repeat
							end tell
						end tell
					end tell
				end tell
			end tell
		end tell
	end tell
end tell