A:AnswerYes m550 is compatible with the 8500 wireless rear surround - https://www.samsung.com/us/televisions-home-theater/home-theater/sound-bars/340w-3-1ch-soundbar-w--wireless-subwoofer-hw-m550-za/
A:AnswerI've seen Samsung’s Radiant360 R1 Wi-Fi/Bluetooth Speakers used with that soundbar, but I've been told that any Wireless Multiroom Speaker from Samsung can be used.
A:AnswerIt does but was very irriated how to get it working and very disappointed in sound quality it really didn't do much of a difference! Very disappointed purchase!