wolfson wm8741 external filter?
 

Hi, I am seriously thinking about making cs8416->wm8741->buf634+opa627 box. My main question is considering wm8741 external filter recommended by wolfson datasheet (page62). Haven't found any information about it could someone explain me in some detail?.. Does it really clean up the audio signal?

So is it worth making this filter? (P.S. I have six spare opa627 for this job)

If you read the notes under the schematic (1) you'll see that the filter has been specifically designed for low noise and needs an opamp with better than 3nV/rtHz noise. The OPA627 doesn't meet this (5.6nV/rtHz @ 1kHz).

Why opa627 won't do the job? As I have read that this opamp is the most musical.

Still if someone could explain me in more detail about this filter how it works.. Why wolfson recommends connecting your amp or preamp through this filter and not directly?