I owned an Sflo2 before but received 2 consecutive defective units and MP4Nation was never able to get me a properly working unit. I compared the 601 side by side with the Sflo2 when I had it and I found the 601 to be superior. I no longer had a reason to keep the Sflo2. Not to mention it took 8 hours to fully charge when it should only take 4 hours. The Sflo2 is too digital sounding (un-natural and fake sounding) when compared to the Hifimans effortless and smooth-organic sound.
Ah, I read about someone who got two defective units and then got the 601 (also defective), so it was you? small forum! I find my T51 combined with the TTVJ slim, makes a very tidy tube like setup, and never feel tired or bothered in long time play for they balance each other, likewise between the Hifiman 601, but I did not get this digital signature your talking about, maybe you needed some burn in (like a year...8 hours to charge) .