My suggestion is still to jump of the whole additional clock train, all together. All the naysayers are correct in one aspect: Digital is always perfect.
The only thing that matters is how much noise/jitter you have in the DAC/Clock and how degraded that conversion step gets due to this incoming noise. (These are Hans B words, not mine of course)
Since the filter solved the problem, it is clear to me that it cleaned up some sort of noise that you had from your gear, prior to the filter. I don´t know why the noise is getting worse after a while but i have to say that i am positive that it is noise, and not about crystal/shapes in the digital signal.
The main reason to jump of the additional clocking train is the added complexity. It does seem to lower the noise floor so i am not saying it isn´t working, but it just presents a level of of complexity that muddies the water when trying to find the root issue.
Just my two scents.
And I am often wrong as well! 🙂
