From what I understand CPL + IR theory does NOT equal ATPL theory for fixed wing but it does for helicopters.
Therefore a CPL/IR for fixed wing cannot be upgraded to an ATPL so you have to do the 14 ATPL exams (as you're not a helicopter).
However, beware that there are a couple of errors in this area in LASORS and the actual Bible is JAR-FCL.
Cheers
Whirls