[Dilettante]

Bill,

Use HDMI cable to connect your 105 to your LG OLED TV. I'm sure your LG OLED TV has multiple HDMI inputs. You said one is used to connect from your Sony 4K bluray player. You can connect your 105 to the other HDMI input on your LG OLED tv.

Alternatively, you can download the Oppo 105 media control app on your mobile device. But you will have to have the Oppo 105 connected to your home internet wifi and have your mobile device (tablet or smart phone) connected to the same home wifi as the Oppo 105. Then go to Oppo website and go to the 105 link and download its mobile app or media control app. With this, you won't have to connect your Oppo 105 to your TV. With using the Oppo 105 media control app you will have access to the same Oppo main menu setup as you would when you have the Oppo connected to your tv display.

On the Oppo 105 main menu settings, go to "setup menu", go to "audio processing", make sure that the "output volume" is set to "fixed" and turn the volume to maximum 100.
It will solve the low gain or low input signal coming from your 105. I recommend using the XLR balanced stereo analog out of your 105 as it sounds better than the RCA single-ended.
I'm sure your Mac MX130 has XLR balanced analog audio input.