J Dilla

If you're happy with the Fiio K7, the Fosi K7 seems like a nice option, but I don't think it's worth switching unless you're really into...

Yep, that 2.7µF capacitor should work just fine for the tweeter. The R1021 and L1021 are probably part of the attenuation circuit...

Opus could be a better choice for saving space while still sounding great. The difference between FLAC and Opus on Bluetooth won’t be...