I've built DAC with pre-amp and headphone amplifier combo several times which surprisingly sound good. Moreover, this might become more practical unit that act as headphone amplifier and can be also connect to home audio system with the same output from the unit itself.
I made PCM63 DAC with this combo here, long before that, I also made portable TDA1543 DAC combo here. The secret of those combo lies on the current output booster that act as buffer, lowering the output impedance which easily drive any headphone or as a signal output to feed the home audio system.
Especially in this post, I will share my latest upgrade for my previous TDA1543 portable DAC combo that I've built last time. This upgrade resulting to better sound quality.