If you never heard a Teac amp I'd suggest trying one out since they seem to perform much better than what the specs say from those that I've tried so far. As I noted above that the UD-301 headphone output only has 100mW I think its a high quality 100mW that it puts out and it seems to have better synergy with more headphones than my Ember or Lyr2 but since I listen at fairly low levels it may / might be under powered for someone who listens at 85dB+ since that about as loud as I can get the HE560 with the UD-301.
The headphone jack of my Teac A-H01 is also only rated at 100mW and its the same when I tried the headphone jack of a friend's UD-501 (100mW), they all sound the same to me and also to the owner of the UD-501 who also has the HA-501 paired with it. The HA-501 is an interesting amp since there is a switch which you can change the damping factor (as TEAC calls it - like changing the output resistance on the Ember) and its like a fine tuning to better match the amp to a headphone.
@koover, can't thank you enough for the tubes / adapters for the Lyr2, they are still in use and I think much better than most of the sub $100/pair tubes that I have.
@phthora, your point on the power versus scaling is a great point that I think gets lost at times since most "powerful" amp are usually seem to be built better IMO.
@Haris Javed I would have been thinking the same as you that the HE560 is under powered with the UD-301 but hearing is believing for me. I hope you get to try a Teac amp since I feel they are under appreciated but it also means there are some great deals out there.