I think you should either place both the 'M' and 'S' switches on the same side of the 'Voice,' or make a larger separation or line border between, for example Voice 1 Solo and Voice 2 Mute. Even though the colors make them clear when they are engaged, when they are not engaged it is sometimes hard to immediately see, again for example, whether the 'M' after 'Voice 2' 'S' belongs to Voice 2 or Voice 3.
Perhaps no one agrees with me ... but I thought I'd bring it to your attention.
Best regards.
DF