Conversion to DSD: Does It Eliminate Digital Glare?

If you are still playing the original file types, and the same dac, then how do you know it's the cables?  I haven't found that cables and room treatments make the slightest bit of difference for this issue.  My SACDs sound great but some--not all-- of my CDs tend to harden up in loud passages.

Herr Mahler, I bought a Sony 5400 ES back about a year after they came out.  I noticed the same thing.  SACD's almost all sounded far better than redbook, with any digital glare type artifacts being rare.  I began to invest heavily in classical SACDs.  After I owned the Sony for a year, I sent it to ModWright.  It came back much better overall, but particularly notable was how much it elevated redbook.  I'd say 65-70% of my redbook cds were within a stone's throw of SACD.  Digital glare was not totally absent from all CDs but was substantially reduced in most cases. Only a few of my redbook CDs remained objectionable.  In May 2014 I bought a Sony HAPZ1.  I was immediately impressed by this unit.  After a couple weeks of burn in, the stock HAPZ1's overall performance was nearly on a par with the modded 5400ES, and I noted that some redbook CDs that were virtually unlistenable on the 5400 were now quite acceptable when upsampled.  I subsequently sent the HAPZ1 to ModWright for modification, which of course, improved it further.
I have owned two Denon players in the past.  Both of them were highly resolving, but also prone to digital glare.  I am also not a big fan of B&W speakers.  I could imagine the B&Ws combined with a Denon might be problematic. 
You have a couple of options.  Since you already own an Oppo, you could send it to ModWright.  For a similar investment, you could buy an HAPZ1.  Based on my experience and overall satisfaction with my HAPZ1, I might recommend that approach. In fact, my Modwright 5400 is rarely used. There was a bit of a learning curve with the HAPZ1, and it certainly takes a while to burn and transfer an extensive library.  The HAPZ1 firmware is much better than the initial iterations, and it is nice being able to browse my entire library via my tablet instead of hunting through a bunch of CDs, no matter how well organized they may be.  

Mahler123 - I've just completed about two years of auditioning different cables, more recently implementing acoustic treatments and lastly, the final repositioning of my speakers.

During that time I have experienced what I refer to as "glare" at varying levels and with each change I made, while playing tracks having various file types (WAV, FLAC, DSD, AAC, MP3 etc.. and sample rates from 16/44 to 24/192.

A few tracks are in a couple of different formats and a couple of tracks were recorded at different sample rates - each seemed to present a similar amount of "glare" with each of the cables tried.

Surprisingly, I also found the level of "glare" varied each time I applied room treatments. I believe the final improvements were due to the reduction in reflected waves bouncing around the room, which would indicate that they too seemed to effect the "glare" that I was experiencing.

Once I had the acoustic treatments sorted - all that was left was to reposition my speakers for a final improvement in "glare"

So perhaps what I was experiencing and believing to be "glare" is not the same thing you are hearing.

From your description - "the hardness in full orchestral pieces" is also what I experienced - along with some very shrill moments on solo violin in the upper register and some really awful moments when sopranos hit their higher register with gusto - they now all seem to have been resolved and sound much smoother and extremely detailed AND - I can play the music at significantly higher volumes :-)

So perhaps we are talking about two different things - but what I experienced during this period on my system - neither the format or the sample rates seemed to make a scrap of difference to the particular degradation in sound that I experienced.

I hope you find a resolution to the issue, because what I experienced was very unpleasant and quite frustrating.

Regards...

Many SACD/CDPs do not play Redbook to its full potential. DSD does not play a part in this, good Redbook playback is due to jitter control and often non-upsampling of Redbook files. Try auditioning a multi bit DAC, that will solve your digital glare problem.

My system is computer fronted, I eliminated glare by swapping my playback software to Jplay. DAC is NOS/Redbook only. Only CD player on hand is mass market from the 80s which sounds like ice. Perhaps it's not the DAC but CD playback?