B&W speakers sounding very harsh?

I think everyone here would agree that trying to grade out a system at 50 hours is foolish. All new components, speakers, cables... need 2,3 or 4 times that much time to effectively burn in to produce their true sound.

Utter nonsense

Ozzy summed it up best. B&W’s greatly overemphasizes the top end. I own a pair.
Thank goodness for tone controls. I have treble pulled WAY back. At higher volume the sizzling returns. My next speaker purchase I’m going for a dark speaker. The older I get the more I appreciate a neutral sound. 

+1 ieales! This "burn-in" stuff gets repeated ad nauseum by the ignorant!

Well when you learn the difference between Break-in (anything BUT valves or tubes) and Burn-in (valves and tubes) then you might be able to offer a suggestion without showing YOUR ignorance about Breaking in equipment.

500+ hours of BREAK-IN for teflon caps. 1000 hours of misery in some cases.  75 or so reports from about 130 customers over and over.. CUSTOMERS mate not frat boy chat in the halls. 1975-2004. I built a few pairs and sets of cabinets. Usually with ribbons or planars or both. 
I liked TNT and a few surplus caps but they were all teflon. 

It takes DC to break in teflon caps, plain and simple, that tiny tickle when firing up is all they get until the caps turn that wonderful tan color.

Everything takes time to settle and break in. The wood, VC drivers, cabinet insulation, dielectric/construct settling.

Every show I've ever gone to, the best in show always brought well conditioned cables and the equipment was well into its service life.  The stuff that sounds like frying eggs, sizzling bacon and BOOMY BS usually got their just reviews..

The "Its perfect out of the box" bunch is fine.

The fact is it just gets better..

I know all cables sound the same, there is no prefer direction, any ol fuse will do, cable cookers do nothing, contact enhancers don't work, ear plug don't work above 130db and horns rules. Thought I do agree Horns CAN rule.

People are not ignorant, delusional or anything else. OTHERS inability to hear. Not, "hear a difference". JUST HEAR at all! Is on full display.

I think OTHERS have demonstrated several time by comment alone, they, cannot hear certain things and or usually HAVEN'T been around enough equipment to tell the difference. 

BTW there are ZERO 24 hour cable reports.. weeks per pair minimum just to settle and somewhat break in.. Months is a more accurate.

Regards

The equipment is run in at the factory as most defects show up immediately. By the time it gets to the customer it is good to go with the exception of some speakers like ESLs and planars that will loosen up a little and the diaphragms equilibrate. Perhaps a few cartridges.

Back to your problem. Your description is a bit vague but it sounds like we are dealing with either sibilance or distortion. Sibilance is easy to stop. If your Marantz has EQ capability just drop 3000 to 4000 Hz a couple of dB and it will magically disappear. If it does you have your answer if it does not we have a distortion issue. If the impedance of the speakers drops too low you might be overloading the amps power supply in which case the only solutions are, don't play so loud or get a new amp that can handle it. Does this problem go away when you lower the volume?