can this amp be used with headphone out put from a normal stereo amp?
I don't see why not, although I would think you'd have to keep the output from the stereo REALLY low to avoid blowing it out. I use four of these things in my video work, taking the audio from a video camera's headphone monitoring jack and running it to several sets of headphones. A camera's audio output isn't very high to begin with, so I haven't worried about the level going into this little amp. So I would be very cautious about using a big stereo amp -- start real low and go slow! Good luck.