Accuphase DAC-50: Glaring sibilance

I updated the user slide-in DAC board from an Accupohase DAC-30 to the newest DAC-50. The brightness is way too harsh.
     The DAC-30 uses two Texas Instruments PCM1796 chips driven in parallel for each channel.  While the newest DAC-50 DAC uses AK4490EQ chips from Asahi Kasei Microdevices in a double parallel configuration per channel."

The only changed variable in my system is this updated, new DAC-50 placed into my Accuphase E-550.

Suggestions to minimize brightness are appreciated-
Any experiences with the DAC-50?    Will burn-in time help?     An outboard clock make sense?
Thanks, Musically, Ken

It seems that I have to wait patiently as it burns in for hundreds of hours. Hopefully that will warm it up to a much more pleasant sound. Hopefully...
Thanks for your respnses
I have never heard the words Accuphase and harsh used together.  That is very surprising.  If you have a return option, I would let it burn in for just under that period and return it if it doesn't get better.  
Thanks Chayro.  I too was surprised to hear such a bright sound form my Accuphase E-550.  I'm hoping that after hundreds of hours of burn-in I will again hear my enveloping, lovely Accuphase music.
  I will post here results after burn-in is complete.  Meantime, I patiently wait.
Please let us know how it sounds after 4-500 hrs. Yes that lovely Accuphase sound.