The sampler board assembled and after adding a couple of minor mods DAC is fully functional, as well as program change buttons.
Display is not updating properly which is likely because of LCD controller vendor being different from the one used in prototype - commands and timings need to be revised.
Testing of traditional MIDI interface is to be done as well.
PCM5122 DAC turned out to be capable of driving headphones directly. Not clear if a separate headphone amp and output makes sense is this scheme. What do you think?