4-port 110 ohm AES adapter. 8500 with any of 8510, 8410, 8415 audio sub modules when all four AES ports are desired requires one per 8500. 8400 with any of 8510, 8410, 8415 audio sub modules when all four AES ports are desired requires one per 8400. 5330 with 6330 audio sub module when all four AES ports are desired requires one per 5330.