I think you would want to verify a couple things first. Does your TV have an analog audio out, (several new models I have seen DO NOT, they only have an optical out).
If so, is that out put Variable or Fixed. I would say in most cases it may be fixed, meaning if you turn the integrated speakers off, the volume button on your TV remote will do nothing to change the sound level of an amp connected to that output.
You may need a small IR controllable amplifier, which means you will either have to program it into a universal remote, or use a separate remote to turn the sound up and down.
See this thread on Electronic Houses sister site for ideas of small form factor amps that may be an option.
My best advice however would be to look at something like this
as it has digital and analog inputs, and a remote for volume etc, and it will mimic your flatpanel profile while increasing the sound quality for a small investment.