You'll have access to any domestic US Club for the cities you're flying from through and to on the day of travel. Just show your Enyov Class Boarding Pass at the desk. Also, you'll get free drinks (alcohol, if you're so inclined) at the clubs as an Envoy Passenger. You'll also have access to the Envoy Lounge in PHL on the departure flight only (many have tried to get in there on their return, and most of us have failed). At Madrid, you should have access to whatever arrivals lounge US uses there (if they have one there).

On your return, you'll have access to the the third party lounge in Madrid and access to domestic US Airways Clubs on your return (again with free drinks).