MORE IMPRESSIONS:
I posted some of this in a PM to another head-fi member, but wanted to say that since I got the DACmini in February I've listened to the LCD-2 headphones more in the past 4 weeks than I did in the previous 6 months because of the improved synergy with LCD-2 over my other amps. Prior to this my $1000 ALO Amphora was my best amp with the LCD-2, followed by the HDP. But the DACmini has taken the lead.
I just didn't have anything with synergy this good with the LCD-2 (I was using HDP > ALO Amphora or HDP alone before). And since I received the DACmini 4 weeks ago I have put maybe only 5 hours on my Apogee mini-DAC > WA6/eXStatA/SAC/EF5 in the bedroom rig, mostly just for comparisons but not personal listening. I've also been using the DACmini line-out > SR-71b > HE-6 about as much as the LCD-2, followed by my JH13Pro and ES5. My basement rig with PS Audio PWD > Woo WES and EC ZDT > HD800, HE60 and O2 Mk1 has been getting ignored too, not because it sounds bad but because the Macbook > DACmini in my bedroom is more convenient.
After spending all this time feeding the DACmini into the SR-71b amp for the HE-6 headphones, the big surprise tonight is that the DACmini drives my HE-6 to normal listening volumes at 2 o'clock, and it plays music at volume levels louder than I like when max'd at 5 o'clock, without having the sound turn south like it's running out of steam. It still has about 4-5 dB less headroom than my balanced SR-71b at full power, but it's power is now closer to the HDP or EF5 with HE-6 headphones vs the lower gain pre-production model shown at RMAF. That's totally useable, although I'd like more power with the HE-6 to improve bass impact just a little, but bass depth/presence is still excellent. So I can't discount the DACmini for people with the HE-6 anymore, and it can always be used to feed a more powerful amp when money becomes available later for an upgrade. The new DACmini PX model with 25-watt speaker amp might be even better for the HE-6 headphones which like to be plugged into the speaker outputs of powerful amps. But for now I'm really digging the CX model with my HE-6.
My SAC KH1000 amp for the AKG K1000 headphones has the extra power for the HE-6, but the aggressive nature of the SAC amp means it doesn't sound as transparent/good as the DACmini because it's better suited for the mellower sounding K1000 headphones. If I didn't want to use extremely sensitive IEM all the time then I might go for the gain of 10 like Austin's modded DACmini instead the standard gain of 8. I just worry that more gain could increase the noise floor and that might make it less enjoyable to use with my ES3X. That fear may be unfounded, but I don't want to take the chances, especially when I have been listening to the HE-6 with it for the past couple of hours with the volume only at 2 o'clock and no urge to turn it up more (nor do I want to disturb my sleeping wife). I still think the more efficient LCD-2 are a better match with the DACmini than HE-6, but this amp can definitely please both camps as well as making HD800 owners happy.
And a few other observations:
1) While the SR-71b has a little better dynamic headroom with the HE-6, I was experiencing some bass clipping and doubling (not sure which) with the HE-6 when using 30Hz test tones and below; and bass notes of 20Hz were difficult to hear while the doubling was much louder than the actual tone. Switching to the DACmini amp and listening to the test tones I find the DACmini does not exhibit this doubling effect, nor any distortion or bass roll-off. I was using the DACmini line-out to feed SR-71b, so it was the same source. The deep bass with the difficult to drive HE-6 is clean and extended through the DACmini, although with headphones other than HE-6 the SR-71b didn't do as poorly. Note - I only use the SR-71b with full-size headphones if they are balanced, and my balanced LCD-2 cable should ship today. The SR-71b didn't do very well with my single ended LCD-2.
2) The HDP DAC line-out made the SR-71b amp slightly more aggressive sounding in the upper mids and highs by combining their similar traits and multiplying the effect. Feeding the DACmini into the SR-71b results in a more refined and balanced/transparent sound out of the SR-71b. So, I am finding the DACmini is a little better as either a DAC or an amp.
3) I used to feed my Pico DAC-only into my ALO Amphora and SR-71b with my Macbook, but switching to the DACmini as the source also results in a more open and deep soundstage, more so with native 24/96 music where the extra micro-detail adds to the transparency, air, and ambience. I am one of the earliest loyal buyers of the Pico DAC, and it's a great DAC for the price and obviously more portable, but I don't see myself going back to it very much in this rig. I like the Pico too much to sell, but not enough to use it in place of the DACmini. If I need a slightly more laid-back sounding amp I can feed the DACmini into my Amphora, and if I want a slightly more aggressive sounding amp I can feed it into my balanced SR-71b. But so far I am quite pleased with the DAC and the Amp section alike.