Just back from Biscarrosse (15nm south of cazaux). Flew north and south through the airspace. Call Cazaux Approach on 119.6. If they are not in, an ansaphone will advise on the frequency (in French and English) if you can transit (but they ask you not to directly overfly the airfield at Cazaux). If they are in they will probably ask you to squawk and then give you clearance into the zome. I found all french atc to be VERY helpful and especially patient with all my requests for status of the red military restricted corridors.
Enjoy, and if you have the time, visit the Pilat Dunes and Biscarrosse Seaplane museum while you are there
