All HD channels the sound is far lower than the SD channels, I have to turn the volume down a lot when I change to SD is this the box at fault or the stations? Are they any settings that can help? This does not happen on freesat.
Tune to a SD channel turn down the TV volume. Using the box remote control turn up the box volume to near max. Adjust your TV volume to a normal listening level.
In the box TV audio settings change the audio output from surround to stereo.
Now tune to a HD channel the volume should be similar to a SD one.