A:Answer Hello GolferTom,
The HW-Q850T would work best with the 75Q900TS. You will be able to use Q-Symphony which is a new level of acoustic immersion accomplished through collaboration between Soundbar and TV speakers. Any wall mount bracket that supports 75" TVs will work, main difference will be if you would like the option to tilt or move your TV. For Cables needed I would recommend a high quality HDMI to get the best performance from your TV. Please check out BestBuy.com.
https://www.bestbuy.com/site/samsung-5-1-2-channel-450w-soundbar-with-8-wireless-subwoofer-and-dolby-atmos-with-alexa-black/6400657.p?skuId=6400657
https://www.bestbuy.com/site/searchpage.jsp?st=wallmount+75%22&_dyncharset=UTF-8&_dynSessConf=&id=pcat17071&type=page&sc=Global&cp=1&nrp=&sp=&qp=&list=n&af=true&iht=y&usc=All+Categories&ks=960&keys=keys
https://www.bestbuy.com/site/searchpage.jsp?st=4k+hdmi&_dyncharset=UTF-8&_dynSessConf=&id=pcat17071&type=page&sc=Global&cp=1&nrp=&sp=&qp=&list=n&af=true&iht=y&usc=All+Categories&ks=960&keys=keys
^Cristian