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
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