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

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. 
@rubinken thanks for creating this thread. Im looking up this comparison for my up gradation as well. Currently Im using DAC-30 onboard slot along with my E-460 Amp.
Im planning to upgrate to DAC-50 onboard slot. Can you please give me a qualitative feedback and improvements that you experienced in DAC-50 over DAC-30. Does the improvements makes a big difference in synergy and listening excitements in terms of Transparency, Soundstage, Low frequency Control and Tonality. Look forward your feedback. 
Rubinken, Can you give us a long-term update/review of the DAC50? Was the brightness simply a burning in issue? I saw that you said it changed, but did it completely go away and are you completely happy?
I am interested in an Accuphase integrated amplifier. I am looking at the E-408, E-450, E-530, E-550, and E-360 as options. I am also very interested in both the DAC 50 card and the AD 50 phonostage card.
Besides wanting to hear from you about the DAC, could you also tell me a little bit about your amplifier? Which speakers are you driving? Did you compare to any other models by Accuphase before you decided on the E-550?

Thank you very much!