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

@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!
Hi Mark,
I had the E550. It sounded *phenomenal*- great soundstaging, transient response & emotionally involving.  I was driving some Consensus Audio Conspiracy speakers from Austria  They utilize six ceramic drivers with total smoothness. (After decades of listening, I feel that Ceramic drivers with Class A amps sounds most compelling to me. Somewhat of a generalization, but tis what it tis.) The phono board sounded excellent to me.  I never ended up enjoying the DAC50. I replaced it with a used AMR DP777SE, which with it's tubes serves me fine.
  I gave my E550 to my son. It sounds fabulous on his Sonus Faber Guarneri Momento speakers as well. It's a terrific integrated amp.
  Hope this is helpful. Enjoy your search and listening, Ken