This macro sorta does it (unrar it to Reaper/keymaps and import it in the action window): It'll solo any item under the mouse cursor within the current time selection, while it's playing...when you're finished you'll need to unmute the items though (just marquee a selection and hit alt-m, that's pretty quick...or make a shortcut). ps it's mapped to F12. edit: arrgh, that won't leave other items 'on' either if that's what you need, sorry...