A script using CTRL+A and 2x(ALT+S) is possible but it is almost just as fast to use the existing SONAR bindings. It takes ALT+S twice, one to toggle all track solo buttons on and one to toggle all of them off. The autohotkey script bound to Windows+S would look like this:
#s:: Send, ^a!s!s Unfortunately I believe buses work a little differently, not sure about a solution for both buses and tracks.