Loads of physical knobs is the most intuitive UI for this kind of thing. You can find the control you want to tweak by combination of it's position and touch ve

Loads of physical knobs is the most intuitive UI for this kind of thing. You can find the control you want to tweak by combination of it's position and touch very fast and in many cases without purposefully looking at the thing. When we tried to build touch based mixing/lighting console (large capacitive touch panels were significantly cheaper than loads of physical knobs and motorized faders even ~5 years ago) we found this out very fast and scrapped the whole project. For synthesizer control, people probably aren't that dependent on using it without looking, but the part of quickly finding what you want to tweak still stands.