I have a 2-channel setup, consisting of an old Superscope R-330 stereo receiver hooked up to two tower speakers. I recently wondered if I could add a subwoofer into the mix for some extra bass, so after reading this thread (link) and several threads found by searching the Beginner's forum with keywords "subwoofer" and "channel", I learned it can be done.

However, I am posting what I consider a "follow-up" because I am still not sure about how subwoofer impedances can affect the configuration.

My floor speakers are 8 ohms. I was given a small 4 ohm powered subwoofer, and I would like to know if there are any impedance problems with directly connecting the receiver's terminals to both the 8 ohm tower speakers and the 4 ohm subwoofer. (Receiver's left channel would go to left tower and also to subwoofer left input; same for right channel. This configuration is the same as "option #1" found in the link I posted above.)

Would this setup work well? Would an 8 ohm subwoofer be more appropriate for this receiver, or would I be able to wire a 4 ohm or even a mid-sized 3 ohm subwoofer in this manner without overly stressing the receiver? Also, considering the extra power needed to operate with lower impedances, would a powered subwoofer be a better choice? (Heh, or am I worrying for nothing? :) )

Keep in mind that my usual listening volume is probably somewhere between "low" and "moderate."