I'll post my impressions now, sorry for not writing a full review, but honestly I'm just too busy right now and I'm going on camp soon. Thanks very much to svyr for including me in the tour, much appreciated.
The bass is awesome, it is very strong for both the sub-bass and mid-bass, much more than what I hear as neutral, so if you are looking for a neutral sounding monitor, this will not be it. From what I remember of the Altone 200, the bass quantity is quite similar, but take that with a grain of salt. It is definitely more than the DN-2000. At times I found that the bass was a little bit boomy, but that is to be expected with something that is significantly bass oriented. It is not the fastest, but it is quute quick and only very rarely did I find it was bloated. The sub-bass has a deep rumble to it, much more satisfying than that of the DN-2000. The bass of this thing is definitely the stand out for me, if you are looking for something with a boosted and deep bass response, this IEM is at the top of my recommendation list.
The midrange however, is not as exciting as the bass. While the H300 that I reviewed a while back was overly bright, this is certainly not the case with the 350, so it is nice to see that T-Peos is listening to our feedback to improve the tuning of their IEMs. The midrange is, however, still similarly recessed, a little more than I would have liked. Vocals especially sound quite distant and I found myself turning the volume up higher than what I normally listen to to compensate for the softer midrange. It is, however, quite detailed, but the the best I have heard. Overall I would describe it as a gradual U midrange and I find it to be on the warmer side of things. It is significantly less sibilant than the H300, a big deal to me - it was the overly bright midrange of the H300 that limited it IMO. It is god to see that the Altone 350 is not as sibilant, but I wished the midrange was brought forward a bit.
I found the treble to be somewhat hot, but it was not too much of an issue for me. Personally I like a slightly boosted treble, so the 350 sounded quite good to me in this area, but it did get a bit fatiguing after an hour or so. After listening to them all my other headphones sounded veiled lol. It is actually very detailed, the double BAs shine though here, not sure if they are the TWFK or something else though. It extends well, I didn't sense any early treble roll off even though Seeko seems to show the 350s have a large dip after 9k or so. Cymbals were ever so slightly sibilant, but once again, personally, I was not too annoyed by it. I'd probably warn anyone who is sensitive to treble to stay away though, they are not warm or polite IEMs and you will likely find it to be piercing and very uncomfortable to listen to.
The soundstage is good, not great. Probably a bit smaller than that of the DN-2000, for $400 or so it is not really that good. I get the impression that its presentation is more intimate rather than expansive. It doesn't stop the imaging from being good though, it is precise and accurate.
Separation is good, but not great, detail is also just ok.
Overall, these are a very solid pair of IEMs if you are looking for a V shaped, fun IEM. I did enjoy these a lot, they are certainly much better than the H300. Would I buy these? No, they are very similar to the 200 frm memory and I do not feel the sound justifies the $400 price tag. Quite frankly, I like the DN-2000 a lot more than these and even the Altone 200 sits better with me. If you are looking or the exciting sound that the 350 possesses, just get the 200. IMO (again, from memory) you will not be missing much and there is a good chance you will the 200 better at a fraction of the price.