I am a regular lurker and sometimes advice seeker who has been using the HD598 and Hifiman EF2A for over a year now. I just wanted to start this thread to point out how great the EF2A is as a beginner level single box desktop amp/dac solution.
I will point out the deficiencies upfront too. It probably has too much gain for low impedance headphones however, once the tubes burn in (at least 100 hours) the painful spikiness goes away. Also, the DAC unit is really basic and it will only handle 16/44 CD quality audio.
However, keeping in mind the beginner level distinction, I think it is a really competent amp/dac offering in the sub $200 range. I would love to hear what other headphones people have tried with the EF2A and your tube rolling experiments. I have shied away from tube rolling till now, but now I am ready to jump in.