Has anyone compared the Headroom Micro + Astrodyne to the O2? To me they sound pretty similar. No major coloration coming from the amps really. You can easily hear the changes in sources with both (if they have some minor coloration).
Neither sound thin/cold or dark/warm. Based on memory the treble on the Micro might be a bit smoother, but not sure. Both seem very transparent to my ears. The Micro might have like a little more body to the sound (like barely detectable). I have no reason to A/B compare them since I like them both. My guess is that the Micro is much more powerful and I like having actual inputs in the back instead of the front! I wonder if there's any headphone out there that the Micro struggles with? Can't imagine that really. Not even the K400 needs to go past 50% volume on medium gain. I haven't tried any of those power hungry Hifiman headphones.
It's really nice having a backup amp for my bedroom that's pretty similar to the Micro! The E9 and Magni definitely were not it. The E9 even uses the same op-amps but they sound much different.
BTW I think the O2 sounds closer to the Micro than the Magni. Magni seemed a bit thin/bright. I don't get that with the O2 at all.