However, the Receiver is 8-Ohm min and the speakers are 4 ohm. Meanwhile, I also have a 25 year old Onkyo TX-2500MKII stereo receiver, which is also 4 ohms, and an 8-ohm Pioneer center channel ...

This article discusses 8 ohm vs 4 ohm speakers and how the typical AV Receiver will handle them. We discuss how to set the impedance switch to get the most power from your receiver.

When in doubt about a 4 ohm speaker's compatibility with a receiver, check with the speaker's and/or receiver's manufacturer. If your speakers are rated at 6- or 8-ohms, and most are, don't worry ...

Is speaker impedance, which is measured in ohms, important? Plus, do you need to match speaker and receiver ohm ratings?

When you put a 4 Ohm woofer in a cabinet that cabinet's impedance would add to the driver's impedance. Thus, you could have a 4 Ohm woofer and still a have an 8 Ohm rated speaker.