Agree torquing with proper tool is always better in general; on a simple fastening like guitar speakers stuff, it usually is just fine to do it by hand also IMHO. First checking speaker frame and fasteners / inserts are all clean and in good shape / straight; make the screws come in contact with the frame, then gently tighten by hand, going one screw & one 1/4 turn at a time in an "X" alternate fashion, same amount of few 1/4 turns by screw total max, stop before you feel the need to force too much.. done.
Challenge can often come from older speakers / fasteners, that are not in top shape and don't allow for smooth fastening; still can be an issue with torque wrench also, as you sometime need to "overcome" some hard point when screwing down if one screw / insert is slightly damaged for ex.