The new metal case is very nice with a professional look when assembled. One bit of advice though - the mounting standoffs for the 2 in 1 board were too long for me because the plug in connections on the top of the board were touching the 2nd connector on the TFT which prevented the case from closing. I just used a nylon nut as spacers with nuts and bolts going straight through it.
I took the signal in and +5v/0V from the connectors on the HifiBerry DAC board. I wrapped the whole little amplifier board in insulation tape and just left it hanging inside. Sound quality is excellent although you need to be careful with volume levels when switching synth engines and/or patches that you don’t blow your ears out!
I didn’t know this headphone amplifier, and believe me, i was looking for it several times, but i always fail to choose the right one. I try several amplifiers modules based in the PAM8403, but i didn’t get a good result.
So, it’s great that you have founded. Could you document your work a little bit more in detail and add some photo, perhaps in a new topic with a good title so everybody can find it easily?