Just be aware that many of the newer Marantz amps are not designed to drive a 4 ohm load...that is one reason they are not expensive.

A speakers impedance load to the amp is constantly changing every millisecond. So, speakers are usually rated with a nominal, or average impedance.

Why is this important, you ask?

My big Focal Utopias you see in the other thread that are in my primary McIntosh system are rated at 8 ohm nominal--but the Berryllium tweeter will drop as low as 2.6 ohms at times!! Holy impedance curves Batman!

You have to have an amplifier that can handle the wicked load thrown at it. Will your speakers still play music with an amp that is capable of 8 ohm only? Sure. But it takes everything out of the transformers and will lead to premature clipping of the amp as well as a tinny sound as volumes increase. (You will notice on a heavy Iron Maiden listening session!).

This occurs in many speakers and is why I will suggest you look at an amplifier that will handle a 4 ohm load and also almost double power (in watts) while doing so.

Take a look at Odyssey amps... HERE
They have a few models and are sold direct--there are a couple guys in the GNO Audio Society running these amps--one of them on a $70k set of Wilson Audio MAXX III speakers. You can also add upgrades to thes amps at the time of the build.

If you want to give me a price range and tell me more about your usage requirements, I will be happy to link you to a few amps. I go to the audio shows around the country and throughout the years and have met most of the designers and manufacturers of hundreds of audio companies over the years--so I keep up with all this stuff and may be able to throw some suggestions your way.

What model are those B&W you just bought? I will pull the Stereophile review from back in the day where they did extended measurements on them and find out the low impedance point on them for you.