CAI's can add power to stage 2 if they are designed right. FWIW... Buschur Racing comparison of drop-in K&N vs. CAI (very similar to Prodrive's):
The car was tuned a little, but the MAF curve was not altered. I trust this comparison (for the most part) because this is where Buschur was evaluating whether he wanted to even bother selling intakes for Subies.