Hmm. Well I'm somewhat interested, but not enough to jump on anything I haven't seen many reviews on yet, or demo'd myself.
"Transparent" is, like everything in audio, a subjective term, and if you consider the fact that everyone's physical anatomy is a bit different, we could all easily be hearing very different things from the same source, amp, phones, etc. So it's not quite so simple as "transparent is transparent."
To be frank, the fact that you've forsaken high-end cans for the HD25 does not add weight to your opinion in my eyes, as I've owned the HD25 and A/B'd them with my HD650: the benefits of the HD650 are palpable to me, and in areas that matter very much for my personal listening preferences, so perhaps you and I hear differently.
The units you've listed also aren't exactly portable in the same sense that the Dragonfly, Microstreamer, and Explorer are; these are thumb drive-sized devices that can be used with OTG cables on phones and tablets, and are very easily pocketable; these DJ-oriented pieces you are posting are generally around 5x7x2, which is close to quadruple the volume.
All in all I'm not saying the items you've posted aren't quality products; more that they don't quite fit in with the kinds of units I made this thread to be about. I wouldn't say it's strictly off-topic, as they are obvious portable in some sense, and I'm sure some people would consider them as alternatives, but they're not quite what I personally had in mind when making this thread.
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How transparent does a DAC have to be to be audibly more transparent than transparent? You've bought music and listened to broadcast TV made on the top end units I mentioned.
Dunno for certain I'm afraid. Even the most expensive open back headphones became instantly redundant the day I first got a pair of active desktop monitors. My best cans now are closed back Sennheiser HD 25 1-11 (80 Ohms). Longtime studio tracking and live performance monitoring standards. Never taken the gain beyond 25% without making my ears hurt. Makes sense. The gear I mentioned is designed to be capable of monitoring in a live performance environment. So it goes loud when required. Very loud.
Can they cope with 250 Ohms cans? Most authorities think so. Check out pro reviews, e.g SoundonSound or pro forums like gearslutz for a definitive answer.