Going to the display should be conduit and then you can change as needed. If you want a passive sound bar you can run speaker wires. If you use an active soundbar then you only need the HDMI. I'd run 2 Cat6 anyway to the TV. Anything to a display should be conduit, 2" preferred.

Except for in ceiling and in wall speakers the conduit allows you to make some of the decisions later and focus on the theater.