1. If you use TV optical output, then the TV volume setting is FIXED, your can neither increase it nor lower it via TV remote control. And also you can't adjust the volume by volume's button on Oasis. You can only adjust the sound from Bluetooth receiving device such as the Bluetooth headphone or Bluetooth speaker via the volume button on headset.
2. If you use TV AUX/3.5mm output, you can adjust the volume either via TV remote control or short press Oasis +/- button or press the volume button on headset or speaker.
3.If you use TV RCA OUTPUT, then you may or may not use the TV remote control to adjust the volume, it depends on your TV. Some TV support this function, while some TV does not. You can adjust the volume either via short press Oasis +/- button or press the volume button on headset or speaker.