B&W speakers sounding very harsh?

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?

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.

I think OTHERS have demonstrated several times by comment alone, they, can hear certain things THAT CAN BE EXPLAINED BY NORMAL PHYSICAL CONDITIONS and HAVE been around AND DESIGNED enough equipment to tell the difference.

Here's a 30 minute cable report from about 2003  ieLogical Audiophilia Redux - after I'd officially retired from professional audio.

IF the Break In Brigade is correct, their systems always suck as everything is always changing. I feel sorry for them not enjoying their systems as they pine in anticipation.

If it doesn't sound reasonably good when you first get it, no amount of break-in or burn-in will transform a sow's ear into a silk purse.

On the other hand, if it already sounds pretty good from the get-go, things will likely improve further.

I am not in the camp that BW speakers are bright.  They reveal the source material, that's what they were designed for. I collect the Matrix series and have the 801 S3 with Northcreeks, 803 S2 which I just picked up, 804 and 805's.  I read many posts said these speakers are bright.  I find them great and depends on the source material and how well one has matched components in their system. A neutral system will show poorly recorded material as bright, the next piece of music can be smooth and another terrible.  CD or vinyl same (I don't stream).  I went into a store and listened to 805 D3 that was hooked up to a high end solid state amp.  It was brutal.  Had to leave the room.  The same store had an 804 D3 hooked up in another room and it sounded fantastic. It's all about synergy and what one puts together.  No different than equipment, one SACD player on one preamp sounds excellent, unlistenable on another one.  So I have matched components to my taste and likes (important).  This is my experience your experience may be different. The beauty of these older BW they can be had for a fraction of new speaker price.  I would love to pick up some of the newer ones but outside of my current budget.  I don't buy only because of budget, not sound quality.  I think BW makes great speakers, old and new.