dangerdan

ProF there may not be a seperate amp , but there will be some sort of resister network that which will match headphones impedance to the amp impedance while reducing the amount power to the headphones when they are plugged in.

As for hooking up headphones to your home stereo , I really cant answere that as there are to many unknowns and its been 30 yrs since I worked in the television repair industry.
Yes, your headphones may work fine on your system, but I dont know the true RMS power rating of your system or headset impedance.

If you are running a low wattage amp its not a big deal, but as power increases it does become a big deal.
Think of it like this.
You bought a brand new HD and added a Nitrous kit running at low pressure without any further modifications to your bike. Depending how you ride it you could go years before any serious breakdown occurrs. Its no different with your stereo modification..

As radio/amp wattage increase so can the possibilty of headset failure.

Google - Connect headphones to amplifiers speaker output

Theres some good stuff there.