Yes, I think you misunderstood this, Pui106. Let me clarify.
What the instruction book is talking about is TV volume control (of your Samsung Smart TV) vs the streamed audio from the TV Adapter. The Toslink (optical audio) signal sent from the Samsung TV to your TV Adapter is a fixed volume digital signal via optical laser light. So if you’re watching TV with somebody else, they hear from the speakers of the Samsung TV and you hear from the streamed audio from your TV Adapter to your OPN and these 2 volumes can be adjusted independently. So if your TV partner likes to listen at a very low volume level, he/she can turn the TV speakers volume down, and you still hear the same (louder) volume level from the TV Adapter to your OPN. That is because the Toslink connection sends fixed volume out and not variable volume out that is tied to the TV’s volume. They control their own volume from the TV, and you control your own volume from the OPN.
What I’m talking about is entirely different. It’s between the volume control of your streamed audio from the TV Adapter to your OPN, and the volume control of your live surrounding sound picked up by your OPN’s mics to your receiver. It’s so that you can hear people or sounds around you ON TOP of hearing the streamed audio if that’s what you want. Or not hear surrounding sound (in case it’s just noisy dishwasher or washer/dryer nearby) while you watch TV. If you use the volume buttons on your OPNs, there’s only 1 set of volume buttons, so it controls both. So if the streamed audio is too loud (like in your case), and you want to turn it down using the OPN volume button, you’ll also in tandem, inadvertently, turn down the OPN mic’s volume, even if you don’t want to. So now you can’t hear live people talking around you while watching TV anymore. So what I was telling the folks on this forum is that the iPhone Hearing Devices setting has 2 separate volume control sliders, one for OPN Mic, and one for the TV Box 1 (TV Adapter), that you can play around with to be able to have better control of these 2 volumes independently. If you use RCA connection to the TV Adapter, that’s a third variable audio input you can fiddle with, in conjunction with the 2 volume sliders on the iPhone, to achieve the best balance. But if you use the optical Toslink audio connection to the TV Adapter, that’s a fixed audio input, so you don’t have a third volume control to fiddle with.