Steeda's tech section used to recommend the stock air system with a K&N up to 350HP. It's gone now since they got out of supporting the Fox era I guess.
I agree that the stock air box with K+N filter works great..I modified my air box by enlarging the intake side, (increasing the dia. and then opened up the fender area to match..) Use the modified air box opening to scribe the fender well area and grind or cut and file to match..Increased intake area by 3". Al
I am surprised they were honest with you. Usually companies like to market their aftermarket filters and sell you more than you want/need. I would try it with conical fliter first, and if it runs bad, switch back to stock.