what should I set my a/v rec to for speaker impedence 4 ohms or 6 ohms I believe it is for minimum impedence.

What you need to know is the nominal impedance of the speaker (4, 6 and 8 Ohms are common). You should select the best match. However with most receivers unless you are driving the speakers at high levels continously, you will not have problems if you leave the receiver at the highest setting even with lower impedance speakers.

If the impedance is not printed somewhere on the speaker, such as on or near the terminals, and you can't find an owner's manual, you can measure the DC resistance of the speakers with a basic multimeter.

Measured across the input terminals, the DC resistance is usually slightly lower than the nominal impedance. That is an 8 Ohm unit usually reads about 6 Ohms and a 4 Ohm speaker reads about 3 Ohms.

Inexpensive meters are sold at most hardware, home center, and auto parts stores. Buy one that has a fairly low range scale for resistance (~200 Ohms or less) and use the lowest range for measuring. Be sure to disconnect the speaker before measuring.