The Sony XBR65A9G sound is quite good, but does not replace the benefits of a full surround-sound home theater system. However, its audio-from-screen sound does offer a significant advantage to those using a separate sound system.
The TV's Settings >> Display & Audio >> Audio Output menu has a TV Center Speaker Mode that routes the center channel through the TV screen, where it can be localized to the part of the screen whose action is generating that sound (as specified in the Dolby ATMOS signal). In this TV Center Mode, the non-center channels are output to the separate audio system, where it can distribute other Dolby ATMOS channels to appropriate speakers. This focus of the center channel to a particular part of the screen provides a sound mapping that external audio systems cannot match. And quality of the TV screen audio is high enough to support most center channel audio content.
Be sure to turn on Dolby Digital Plus output, if your external sound system supports that protocol. The same is true for eARC mode (extended ARC), if you are using an HDMI cable to connect to your output sound system, and that system supported eARC. And be sure that eARC cable supports high-speed data transfers (at least 28 Gbps is desirable). The new HDMI 2.1 cables now support up to 48 Gbps signals, and are less expensive than earlier, slower HDMI cables. HDMI 2.1 is supported by this TV.