Maybe too detailed

I would try three things:
A powerline conditioner for the CD player and DAC only.
Even a cheaper used one could do. $100. or so.
Second, maybe a different connector. The cord between the CD and DAC may be wrong for the combo. If you are using a RCA wire, try one that is longer. any RCA 2 meter, give it a try. Or, if it is a toslink connection, try a different one. (also less than $100.)
Third, some ferrite 'claps' around the DAC output RCAs. Cheap from Radio Shack etc, ($25.)

Here is what happened to you:

You lowered the digital jitter so that the detail and HF extension is in focus as opposed to out of focus. This removed the masking effect of the jitter than you had before. The result is that the new clarity is allowing you to hear the sibilance of another component such as a DAC, preamp, amp or even cables. Maybe even your speakers. You need to swap other components in and identify the offending piece(s). Most likely your DAC is at fault.

Steve N.
Empirical Audio

Agree with Photon46--all reports are that the CEC transport has a softer presentation than most, which is why I bought it. That attribute is apparently being overcome by something else, perhaps the jitter scenario described by Audioengr, which is my suspicion. Frankly, the sound resembles the overly bright and etched all-Tact system I heard at CES two-years ago (which resembles, in my opinion, the all-Meridian systems that I have heard). I assumed my tube amp would compensate for the overly digital all-Tact system sound. However, it appears the old transport, perhaps because of design or age, was resposible for the softening effect, not the tube amp. While I dislike the sharpness of the Tact 2.2XP, it does amazingly fix the room problem which was several significant 5 to 12 db humps in the sub-200 hz region that created a dull, diffuse and chesty quality in the sound. Everything immediately comes into focus when the correction is enabled. My speakers may also be partially contributing to this--they use Scanspeak Revelator tweaters which can be somewhat strident in the wrong system, which perhaps I have.

I agree with Steve. I've experienced similar issues. A good pre-amp/amp will, no other word to say it, ruthlessly expose weakness in the DAC. IME, you can either upgrade the DAC (and I haven't done sucessfully done that yet because so many DACs sound similar) or go back to masking the sound. Masking the sound isn't such a bad thing IMO if it gives one a break from the merry go round. :}

So get this--I just put my old Placette passive volume control back in (instead of using digital volume control on Tact 2.2XP) and it took enough of the edge off to make things enjoyable again. Still incredibly detailed and transparent. Would still like things a little warmer, but it's at least a temporary fix.