Your TV likely has two way to connect to a surround sound system.
You can use either the optical audio output or HDMI-ARC to get audio out of the TV to a HTS.
If the surround system also has a blueray player built in then the HDMI-ARC would make more sense since that single HDMI cable will get video to the TV and audio from the TV. Make sure that the system you get has either or both of these. The TV manual will tell you how to turn it one and configure it in the TV audio menu,
Your DVD/VHS stays connected to the TV.