Coupling Capacitor upgrade? Which one first?

.9hz -3db with the 4.7uf cap fine, just bridge out the dac cap.

Cheers George

I didn't like the scratchy noise while I moving volume pot when I removed the dac output caps. I am planning buy an headphone amp which have not input caps. This can be problem. 

I didn't like the scratchy noise while I moving volume pot when I removed the dac output caps.

Sounds like you have DC at the pot... is the amplifier AC coupling downstream of the pot? A small DC offset in the low level signal will most likely result in pops and clicks from switches and pots. A large offset would likely be the result of a failed component or poor design/construction - that could result in distortion or component failure. Where you really don't want an offset is on the output of the power amp as you may damage your speakers.

DC blocking caps should be rated so that they are effectively a short at audible frequencies, so they have little if any impact on the sounds you hear. I'm not sure how much mileage there is in swapping out coupling caps as they are one of the more benign components in audio circuits. But if you really don't like caps then you could look for components that use DC servos instead - they provide protection from DC but are more complex and use more components which means they are more prone to failure.

Volume pot is between rca input and input coupling caps of the amp..

I read lots of comments on the internet about caps between dac and amp.
Generally people have tube amp(only have interstage and output capacitor) & dac(have output caps), they say dac output caps have large impact on the sound..
Scientifically, it is not meaninfull.. 
Even I really doubt boutique cap manufacturers design their capacitors based on pure science.. 
Everything so confusing. 
I read a review saying Jantzen silver z cap have much more detail than jantzen superior z cap. Manufacturer says only difference is silver z cap just uses silver leads!!
There are lots of experienced people in this forum(I am guessing :)
Still there isn't any real answer to my question..
I also thanks to people trying to help me.. 

Even I really doubt boutique cap manufacturers design their capacitors based on pure science..

Many "design" their caps just on the re-labeling of caps like Solen, get some of the data sheets and compare dimensions lead length ect ect of some of these boutique caps to Solen you’ll find identical data between the two. Just the price is 20 x different, just like what goes on with the boutique snake oil AC mains fuses.

Cheers George