For me, the ideal headphone for the DACmini CX is the Audeze LCD-2.... It must be a matter of synergy - where the DACmini CX just "gets it right" with the LCD-2.
I have to add, that HeadphoneAddict (Larry) once wrote that if he had to sell the majority of his headphone inventory, he would not part with his DACmini CX and his LCD-2 (nor his RSA SR-71B). It was his experience and affection for the DACmini CX for use with the LCD-2 that led me to buy the DACmini CX....
I typed a big long post and lost it, and I'm in no condition to type it again. Sorry.
Agreed to always having the DACmini, especially for my orthos like LCD-2 and HE-500 and all my IEM. It seems to be great with everything including all my IEM, but I though that the T1 and HD800 need a little more warmth from an amp (but it's better with HD800 than T1, which is why I didn't buy a T1 after trying it out). Keeping the SR-71b isn't nearly as important as the DACmini.
The SR-71b is slightly warmer and darker sounding than the DACmini, and sometimes with the orthos the SR-71b might seem to have a little more low-end punch; but overall it's not quite up to the same level as the DACmini although surprisingly good for such a small portable amp. I feel like I get slightly less ambience and air out of it with my LCD-2 and HE-500. So, I use it mostly for my balanced HD800 with Black Dragon cable to tame the slightly fatiguing nature of the HD800; but the SR-71b could be replaced as my HD800 amp with other amps, such as my WA6 and the right tubes or with the ALO Amphora.
Since the Nuforce DAC-100 is better with HD800 than my other mid-level amps, that could take the place of the SR-71b, but it's frustrating that it lacks the analog input or the power of the DACmini and SR-71b. And it has a bit of hiss with low impedance IEM or sensitive full-size phones. So DAC-100 is not nearly as versatile as the DACmini in how many headphones it has synergy with. DAC-100 sounds a lot like the WA6 with almost as much power, but the WA6 and DACmini can be used with IEM unlike the Amphora or DAC-100 that hiss. That's why WA6 is still on the list of possibilities to pair with DACmini as source HD800.
The Nuforce HAP-100 is also very good with HD800 and has analog input, sounds slightly more forward than DAC-100 with power that fall closer to the DACmini - but it's output impedance and hiss is still too high for very sensitive IEM although it's noticeably less than the DAC-100. So the HAP-100 might still make the cut over the SR-71b, but it isn't quite up to replacing the DACmini for everything. It's also not as good with HE-500 as the DACmini, although with LCD-2 it's closer. I'd say the HAP-100 is a closer match to the WA6 with HD800, better with LCD-2, but neither is as good with LCD-2 or HE-500 as the DACmini.
Overall, the DACmini is just such a well rounded jack of all trades, and even with the HD800 it's very enjoyable. At the 2011 RMAF show CEntrance borrowed my HD800 at their table to demo the DACmini, and it cleanly beat out the Beyers they had there. I still wouldn't use DACmini for the original HE-5 orthos or the current HE-6 (fairly underpowered with either which makes these 2 phones brighter and less punchy).
So, I could trim my bedroom rig down from 20+ pieces of gear that I rotate through, down to the DACmini + one amp. The main rig in the basement is tougher to thin out, but I'd be happy if all I had was my Perfectwave DAC feeding the KGBH, ZDT and EF6 amps. Between those three amps I can enjoy every headphone and IEM in the house including a couple of vintage normal bias stats (the ZDT is driving a transformer through the speaker out for those). That means only parting with the KGSS or Marantz 2240 receiver down there.