OFFSET linked to another workbook

[robertgrumbles]

Hey all,

I know this question has been asked before, but couldn't find the thread. I need the following formula converted to work across unopened workbooks. I know there's a way to do it with INDEX, but can't figure it out. Any help is greatly appreciated.

=SUM(OFFSET('[ABC.xlsm]Page1'!$D15,,6,,3))

the numbers 6 and 3 are actually variables that need to be able to change.

Thanks again in advance!!!