I got the Beta because I heard it at a meet with LCD-2, and it sounded pretty good. I don't have a headphone amp that provide lots of power, and decided to go with this one because it's regarded as one of the best amp design and in the DIY thread, people build the Beta for LCD-2 or 3(or planar magnetic phone), and I bought a 2 channel version from somebody here since I wanted to get Planar magnetic phones. I have A/B'd LCD-2 with O2 and Beta 22, there is noticeable control to the sound on the Beta 22. On the Beta 22 using my HE-6, if I increase the volume(voltage) it doesn't change the loudness much, but it increases the bass and I hear more details in the sound. I think the additional power increases the dynamics. Sonically, it's the best I've heard, I had no idea that HiFiMan has some great phones(I always through it off because it looks kinda ghetto, never judge the book by it's cover).
I thought I listen at loud levels, but maybe not relative to some members here. HE-6 is plenty loud on the O2 amp. I personally think the sound quality of the ODAC/O2 is attributed to the ODAC.