TOPIC:

I have some very old bookshelf speakers I intend to use as a test run for retrofitting with a PWR-ICE (one each speaker). The manual seems to suggest I can drive the woofer and tweeter independently if they are 4 ohms, or I can have one channel of 8 ohms. Is that correct?

The speaker is rated at 8 ohms, and has a woofer and a tweeter. How does the impedance of the woofer and tweeter relate to the external impedance? Are they in serial so each is 4 ohm? I am a physics major but no idea about the engineering. More practically: can I just grab old two way speakers off eBay and drive the woofer and tweeter using the two channels of the ICE?

Thanks!

No problem, your Power ICE can drive either 2x 4 Ohms, or 2x8 Ohms or even 4 Ohms+8 Ohms or anything you can imagine.
Concerning your speaker, it has a passive filter wich seperates woofer and tweeter form the impedance point of view. both your woofer and your tweeter is 8 Ohms individually. You just have to remove the passive filter and connect each driver to one output of the PowerIce.