I found the dimensions of the Euro round filter, K&N #E-2022. Based on the specs, it should have the similar surface area than the P4, which is also the similar surface area for the filter in the new aFe Magnum Stage2 Intake. According to aFe, the increased air flow area is about 56% more than the flat drop in filter.
The issue with the Euro Airbox is, it does not increase the air flow inlet track size. We now have three versions of modified intake:
The BMW Performance Intake,
The Dinan Ram Air Kit, and
The new aFe Magnum Stage2.
All three of them increase the size of the air inlet tracks to accommodate the high flow air filters.
However, I think only the Dinan style intake will work with air scoops, if you use the air scoops. The other two have vents which will bleed out any added air pressure (however big or small it maybe) generated by air scoops at highway speed.