Coupling Capacitor upgrade? Which one first?

I agree with all of @georgehifi 's comments so won't repeat them. The only thing I can think of that could affect the sound is if the roll off is close to the audio frequencies. Seeing as all the MKS2 caps come with the same pin pitch, you could try the 10µF version (which would move the roll off further away from the audio frequencies) although I still doubt that would make much difference.

+1 for 10uf
Bass will go down another octave "if" it was cutting off a little too early with 4.7uf

Cheers George

Amplifier input cap isn't related to cutoff frequency in this chip amp. (cutoff frequency determined with feedback cap and feedback resistor value wrt to datasheet).
I begin to guess amplifier input cap is much important than dac output caps(if amp doesn't have input cap, then dac output cap becomes have same level importance).
Just I wanted learn you/someone have similar conclusion..


I also don't understand why manufacturers don't have any info about their capacitors. 
I don't expect too much thing from a capacitor. Enough clarity with vocals, good soundtage stage info, good bass, neutral, coherent, neutral tone.. 
Basically it should be transparent(in my perspective it is The same thing with clarity).
I don't know what these words mean in science.. 

Amplifier input cap isn’t related to cutoff frequency in this chip amp.

It will relate to the low frequency cutoff with input impedance of the amp.
If the amp is 47kohm input and the cap is 4.7uf then the bass rolloff is -3db at .7hz (a good figure)
If the amp is 1kohm then it’s -3db at 33hz (not good, bass light) and I’ve seen some chips amps with 1-2k input impedance

Cheers George

Input impedance is 30kohm wrt datasheet.