The 7506's isolation from external sound is no good, but its loud enough for live use...but sound will leak out to outside from your headphones too, if you push up your levels.
The 7509 is a bigger more comfortable and much more powerful set, worth the money if you can afford.
AKGs are extremely extremely accurate studio units, it is for studio recordings, indoor monitorings and precise EQing. The frequency response for most AKGs are almost a flat line, but AKGs not very suitable for outdoor use, the construction and design will inhibit you as it is difficult to squeeze into a cramped bag.