I wound up buying this amp on the forums about a week ago. So you can take me off the loaner program list. Or if someone else wants to take my spot, that would be fine.
I guess I might as well leave some impressions. I currently have the Xin Reference as well, and I imagine many of you would be interested in a comparison. I can't offer what some members can in the way of eloquence in description, but I can offer a few thoughts
They have a similar sound signature, they are both of the "laid back" variety. both warm, yet also very resolving, not overly lush or slugish. So I think they are both contenders for people looking for a tube-like sound in a small package. I'll list some differences between the two.
the Xin Reference's non-sonic advantages over the millet are that it exhibits no tube rush, it's lighter, cheaper, and more durable because of the lack of tubes. It has an airyer sound, a lighter and more transparent sound. It is slightly tube like, but it is not as full or liquid as tube amps i have heard. It has some of those characteristics, esspecially in the midrange, but the treble can only be described as silky. It is precise, but just sligtly rounded off for a nice smooth finish.
Both amps have similar bass, warm, and full, but very controlled. The edge might have to go to the Xin on the control department.
The TTVJ Millet Hybrid has a slightly bigger soundstage than the reference to my ears. It has a similar "tube-like" sound to the reference - i say tube-like because it has a lushness to it, but like the reference has many characteristics of solid state precision. It has a fuller sound than the reference, esspecialy in the lower mids, which are rich, and win over the reference. It has more "weight" and body to notes, but less air, and less transparency than the reference. more of a liquid sound. Treble is smooth, but doesn't have the silky quality of the reference.
In listening to the amps, I dont think there is a clear winner. It comes down to personal taste, intended usage, budget, and synergy with your headphones. I thought the reference sounded better with my HF1's, while the ttvj millet sounded better with my higher impedance AKG K500's (K501's). I dont know if this is because of the tubes giving the akg's extra voltage, or just synergy. The more full midrange, and lower midrange of the ttvj millet definitely helps round out the K500's. I would imagine the ttvj would be a good portable option for K701's as well.
Hope that helped. Sorry for the flowery descriptions
edit: I forgot to mention a reallly nice feature of the ttvj millet hybrid. The way the volume knob adjusts the gain. From all the way at zero, to about 11 ocklock it raises the volume real slowly, so that at 10-11 oclock is not loud enough with my K500's. but then as soon as you get past 11, the rate of gain increases mightily. It is as if the amp is saying "you want power? Here you go! Ive got plenty to spare" I don't go much past 12 oclock with any of my phones. This makes the amp incredibly versitile to headphones with different impedances, the first half gives it enough sensitiviity for iems. i imagine iem users and HD650 users would both be comfortable. Not sure about tube rush with super low imp. phones though...