4ohm or 8ohm on B&W CDM-7nt?

Your speakers are 8 ohms, use the 8 ohm taps from your amp.

I have both 4 Ohm and 8 Ohm output taps on my amps and I simply tried each to see (hear) if one was better sounding. Indeed the 4 Ohm sounded better on my Focals and I rarely, if ever, doubt my completely reversible decision.

Why not try them both and hear for yourself?

i wouldn't even think of connecting 7nt to 8Ohm taps. if there were 2ohm taps like in mcintosh i would connect them there.

“I figured I should be able to get a decent answer here.”

Sorry to say that so far you have not. The first 4 replies apply to tube amps or a Mac with autoformers. I assume you are talking about the 4 ohm/8 ohm switch on the back of your solid state AVR receiver. 8 ohm is the proper setting for your speakers. Refer to page 9 of your owner’s manual, or if you don’t have one, it’s available online. Not sure, but there may be a very slight drop in volume in the 4 ohm position, but DO NOT switch with unit powered on. Also, DO NOT use 4 ohm speakers in the 8 ohm position.

Using 8 Ohm speaker at 4 Ohm connection is OK tho

"DO NOT use 4 ohm speakers in the 8 ohm position."

Yep, it will cause a rise in distortion. Just like the early B&K ST-140.