Hi Nigel, You can adjust vo volume with command-control-option, move with left or right arrrow to volume, use up and down arrow to adjust temporarily and you can also save it but I don't remember how.
you can adjust system volume in two ways: 1> use the volume up and down keys on your keyboard and this may varry according to your keyboard but they make a clicking sound as you press them and I believe this is temporary. 2> open /applications/system preferences/sound and choose the input tab. you can also get to the system prefs menu by opening the menubar and moving down from apple to system preferences. Once in the output tab, you can adjust the volume there. To make the vo changes permenant, you can go to voiceover utility with control-option-f8 or a couple of other places and find speech in the tree. tab through and you will find volume. You can also mute speech and sounds if you like.
