I just made a major update to this review:
UPDATE 10-5-07: I received from Mrarroyo a D1 with better op-amps, as follows:
AD8656 in the DAC (replacing the AD8616)
LM4562 (2) as a buffer in the Amp (replacing the NE5532)
OPA2111 in the Amp (replacing the AD823)
Well, the D1 sounds MUCH better in this configuration, which will come as no surprise to anyone who has been following the gargantuan D1 thread. It's better in EVERY conceivable way. And I mean EVERY way. It's almost enough to convince me to roll op-amps. iBasso itself is coming out with a version of the D1 with better op-amps, and it will be interesting to see which ones they choose. There are SO many configurations. But in this config, the D1 is very good even just as a headphone amp from the analog input. It sounds great. I still slightly prefer the sound of the Move, for the D1 is still a little more aggressive and the Move slightly smoother while being just as detailed, but it's now very close.
And in USB DAC mode, the already very good sound of the D1 just gets better. It sounds terrific in this mode - highly enjoyable. It's now smoother and more transparent than the sound I described above using it as a DAC.
I'm not sure what the total cost is now with these upgrades, but the D1 is quite good. The Meier Move's USB DAC is just not it's strong suit, as the below will show...
ENTER: the Leckerton Audio UHA-3.
Well, this does complicate things a bit. The UHA-3, which I have just added to my portable amp review, is an excellent sounding amp, and it contains an excellent USB DAC. As an amp, it's better than the stock D1 by a WIDE margin (although not as good as the Move). It's very close to the modded D1 used just as an amp. The UHA-3 is noticably warmer sounding, which will appeal more to some listeners than others, but I loved it, and many will prefer it's sound over the D1, even modded, although I think overall the modded D1 as an amp only is slightly better.
But as a USB DAC, it's still very competitive with the D1. Again, different sonic signature. VERY different from the stock D1, which seems cold and aggressive compared to the UHA-3. The Modded D1 as a DAC is better sounding than the UHA-3, but only by a fairly small margin. The UHA-3 again is warmer and smoother, while offering just a little less detail and treble extension, and being just a tiny bit less transparent.
But the UHA-3 is quite a bit less money than even the stock D1, and certainly less that with a bunch of new op-amps. So it's quite a toss up - the UHA-3 is the better bargain in my mind for someone who wants a battery powered USB AMP/DAC combo. It's also FAR smaller and lighter than the D1, but of course the D1 also has optical and coax digital inputs.
Decisions, decisions, for the potential buyer. It's nice to have choices! My opinion is, though:
STAND ALONE AMP: Move > Modded D1 > UHA-3 > Stock D1
USB DAC/AMP: Modded D1 > UHA-3 > Stock D1 > Move.
And there you go.