Coupling Capacitor upgrade? Which one first?

Solen is one of the largest cap manufacturers around, that do Hi-end audio caps.
I’m not going to name the brands that I strongly suspect of doing re-badgeing work, you’ll have to look for yourself on the data sheets and compare all the parameters, it will be obvious.

Cheers George

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

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

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

Cheers George

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

Cheers George

What do you think which one is more important caps, amplifier input or dac output?

Just leave the amp ones in, and leave out the dac ones. But then only use that dac with that amp!

Cheers George

Not too much change. (just a feeling some thing removed :)

Shows you the Wima's are pretty transparent, just leave them be.

Cheers George

Second thought, since you have a non polarized 63v cap on the input of the amp, just bypass the one on the dac (direct couple it) there’s no need for it, at least you get rid of one "pita" cap.
But make sure you power up the dac first then the amp.
And turn off amp first (wait) then turn off the dac.

Cheers George

What's in place at the moment make/model/value uf and volts, polarized or non-polarized 

Cheers George

Still I don’t understand why wima caps aren’t good enough.

They are, I would suggest save the money and look for a "direct coupled output" dac with TDA1541 or better still PCM1704 even 1702.

Cheers George