A mini review of the xDuoo MT-602: for what it's worth, sound signature between using just the Tempotec Sonata HD Pro, the Sonata through the xDuoo MT-602, and just the Apple Dongle and Apple Dongle with MT-602 was exactly the same (and this is with volume matching). Maybe the bass was a little more smoother and warmer while using the amp, but I am not sure even with back to back listening tests.
And this is basically what reviews stated as well - on stock 61J tubes, the MT-602 doesn't behave like a tube amp at all, but rather just like a solid state amp. Which I'm perfectly happy with, since I mainly wanted an amp to be, well, an amp. Plus this presents opportunities to make me even poorer by luring me into tube rolling ;-;
Small follow-up on the mini-review: After a bit more back to back testing, I can definitively say that there's a subtle but consistent improvement in bass quality (bass feels "fuller") and quantity (even at lower volumes, ie, within the bounds of the apple dongle and tempotec, bass seems to be much better present) with the amp over using just the apple dongle or sonata hd pro when volume-matched. The highs are a bit more mellow, but at higher volumes can still become fatiguing quite quickly (as usual), so no mellowness in the upper range provided by the amp. Plus, there is tangibly more "instrument separation" I suppose, though idk if that is the correct term for it. Maybe soundstage is the correct term, but overall I can distinguish various layers and sounds even better than through just the dongles (although the space in which I can distinguish them seems to be largely unchanged).
Anyway, volume matching is fine and all but it shines when I actually make use of it, and boy does it shine bright. My source volume (Windows 10 WASAPI shared with custom eq via Equalizer APO through Peace with a -9.5dB preamp, or ALSA via Manjaro Linux without any eq) stays at 100%, tempotec is at 3 levels below max volume, and with these 2 set up in this manner, I don't need anything more than 1 o'clock on the physical volume dial (which itself fricking joy to use; it's so damn smooth and velvety!), and usually stays at between 9 and 11 o'clock. Anything over 12:30 is too loud to listen to for more than 20 seconds or so.
Adding everything up, I won't say the sounds feels coloured in any way at all. All the above are quite subtle improvements, and it took me a good 3-4 hours of back to back listening to even be sure of them. Shouldn't matter to most people; if anything, it's overall better in all places. Albums used were
Hollywood's Bleeding,
Barfi,
Rockstar, Manchild and Songs of Her's, along with various other tracks, to a Hifiman HE400i ver. 2020.
Overall I'd recommend the xDuoo MT-602 without doubt to anyone looking for a non-portable amp under 10k, although do keep in mind my experience of dedicated amps is limited to just this one lol. Make of that what you will