The H/K AVR-635 only has speaker input for 8 Ohms, and that is at .07 THD 20-20K @ 8 Ohms (according to the online manual). You might want to find out directly from a dealer if you can do 4 Ohms safely. And then dedicate a house fan to cool it if you are able to drive it at 4 Ohms. Also, remember that your THD will go above 1% easily, which is audiably detectible.