Sony DAV-C450 home theatre receiver

[jameslkieb]

They're harder for the amp to drive but not in a bad way. You'll just get less volume out of them. Going the other way can get you into trouble. If your amp can't handle driving say a 4 ohm load and you hook a 4 ohm speaker up to it, you'll pull too much current through the amp and risk blowing it. It usually sounds pretty bad too.

[jameslkieb]

Oops, to answer your question, if you can build a multichannel amp into a small package and drive your own 3 or 4 ohm speakers with it then you're saving a lot of power and money.
Typically most drivers in a box are 8 ohms and some older ones are 16. If you run these off your typical HTIaB it'll sound a lot quieter than the ones that came with it.