here how to do it:-
turn yur amplifier and you can see 4 output ports two black and two reds
what you have to do is called "bridging" .you have to join the two black ones( dont join the red ones)
then add your speakers as usual as you did..(two in black and two in red)
if there is a fluctuation in sound or your amplifier get heated(in rare cases) seperate the joint between black ones
if this doesnt work for you then go to some narby electronic shop and tell him to replace the IC of your amplifier with some powerful one like STK or DOUBLE STR..
and last thing if you want a powerful sound try some custom speakers.
if your amplifier is powerful and you add your TV speakers there no use..