ok. still recommend getting hold of Eric's set of templates, and then open them up in the Novation RemoteSL Editor, and have a look at how Mute/Solo is dealt with - i can't remember if it's sysex or midiCC ... probably a sysex message, so you'd need something that sends sysex - in which case, the project you showed with the Arduino would be worth doing, if it's just a mute/solo box, but you'd have to study that video a bit, and how to code it - didn't look too difficult - and then you could make a? little DIY box. honestly if you're worried about a phone getting stolen, wouldn't you also worry about a QY70? anyway, those templates are the key to knowing what you can and can't access remotely. if you master the arduino thing, you might be able to do some cool things like edit effects sends, etc.
alternatively, you could just send midiCC 7/volume for each midi channel, and then you'd be able to look at lots more midi controller boxes.
