electric guitar ---> stereo = wrecked speakers (from experience)
Once upon a time I bought an amplifier from an electronics shop, dead cheap, about the size of a fuzz box, needed to be soldered together.
Output volume was similar to that of an acoustic guitar, so the neighbours were happy.....
......but anyway, iMovie has a record option, maybe you can use that to hear what you are playing.
Don't blame me if you blow something up.