Anything with volume feedback gets a slider. Just tap the volume screen to bring it up. If your device has no volume feedback, there’s no way to create a slider.
Apple TV is an infrared device, so that would involve crazy macros with lots of left-left-right-up-down-up-down nonsense. We don’t recommend it. Roku is IP controllable, has great Netflix support, and has a command to jump directly to Netflix.
For the Oppo 95 feedback, assuming you are using serial as Oppo does not provide any feedback yet via IP (they say have a plan to do so in the future), you need to send ‘RS232 VERBOSE 3’ per the Serial Compatibility page. Once that is sent, the feedback comes alive.