MIXING DESK

MIXER.
My last posting was to enquire if it was possible to mute a track or tracks during playback.
The kind reply I received drew my attention to the Mixer Palette.
The piece Music is for a Bb Cornet, a Harp and a Cello.
I have disregarded the MIDI section because I think that it is only the synthesiser settings that apply to this piece.
At the top of the Mixer page there is a ticked box which has next to it ;-

                                                               <   " play part only "  >

I have tried clicking on it to see if there is an alternative, as there usually tends to be with such boxes, but it stays ticked whether clicked or not. ( Since it doesn't change... I am wondering what it is there for ? ) I also noted the 300 different instrument Sounds whose names scroll down in the Window called

                                                                          <  " Sounds " >

Initially I set the Volume and Pan to around halfway
I clicked on the last 3 of the 4 visible buttons, which creates a green, orange, and a purple square numbered 2, 3, and 4 to appear.
Concerning the red and green lights at the tops of the faders, I clicked on the Green light ( 1 ) to Solo the first track, the Bb Cornet.
The Harp, which is notated on both a Treble and Bass Stave seems controlled by Voice 3 whose Mute switch I illuminated ( in addition to ensuring that the Orange square in the line of the 4 Mute Voice buttons is coloured in, depicting that it is Mute as well)
.......................................................................................
Now for the difficult part.
During various playbacks I used the < " Sound " > Window in the Mixing Display to give me access to the 300 other instruments that the Synthesizer creates.
To my delight every single instrument came up immediately and I received an extremely good impression of what the sound would be if it had been Scored with a different Melody Instrument.
I decided therefore, to try out other sounds for the Harp Part that I had been using as an accompaniment.
In The < " Mute Voice " > Section of the Mixer I duly clicked on 1 and 4 to bring up the Blue and Purple Squares.
It seems that " 2 " represents the Harp.
I then illuminated the Green Light to solo the Harp and activated the Red to to Mute the Cornet and the Cello.
Checking the playback I found that this worked fine.
The Harp sound was the same.
To introduce other sounds, I stopped Playback clicked on " Rewind " and re-set the scrolling list of 300 instruments.
I chose one Sound after another in this Trial, but the Harp sound stayed the same no matter what the readout in the Window was,
It is as if that facility to Mute ( and change the sound of ) Parts is not available to me beyond the First part, the one for the cornet.
I can make no further changes to the Mixer that I can see, so I am wondering if this version of Muse can do this at all, or, is there something I am overlooking to bring about the changes in Sounds that I am seeking.
May any of you Forum Members help me here please ?

Sam Waylen