As far as I have heard (4 friends took the test in different centers), none of the centers in US provide head phones. Everyone of them complained about the quality of the speakers. I believe all IELTS centers have crappy speakers. There is no incentive for them to improve their services, they are merely coaching/tutor centers that get the license to conduct IELTS. These are not IELTS offices run by British Council/University of Cambridge, think more like a franchise.
IELTS centers do not even provide you with your own sharpener for the pencils that they give you. Asking for extra pencils or paper will only cost you time, they are not particularly nimble on their feet!! Again they don't care.
If hand writing or listening over crappy speakers is an issue, think about CELPIP test. It's a fully computerized test but has only 2 centers in US (NY and Seattle).