Can't argue there really, that there's a compromise with these small cheaper T amps with a headphone output as well. I guess that's partly the reason why the TP20 is said to be a bit better sounding. I went for the TP21 over the TP20, because at the time I still had my X-Fi sound card, so just connecting the amp to that and then the headphones to the amp, seemed like the solution with the least hassle at the time without having swap between headphone and speaker amp. 
X-fi ended up popping it's clogs and I decided to go with a DAC/HP amp, rather than another sound card, so I probably should have just gone with a TP20 to begin with.

X-fi ended up popping it's clogs and I decided to go with a DAC/HP amp, rather than another sound card, so I probably should have just gone with a TP20 to begin with.
