So after a little bit of tip rolling, I'll post some really quick, raw impressions of the Tzar 90 (with my background in this tier being mainly the SM3):
The comfort is awesome. I really love these IEMs in my ears, and if they somehow made a large bore Shure olive, I'd be in heaven. The included tips seem for the most part fine with me. I have a blue tip on my L ear for comfort, and a red tip on my right ear for rigidity. My ears are weird like that.
The sound signature......well, I want to say it's a V shape, but not a huge dip with other cans I've tried. I'm having hard time really figuring out this little guys sound, and I feel that part of it is listening bias, coming from arguably one of the darkest mid-centric IEM's made. I feel that this is a warm IEM like Wizard says, but isn't mid-centric, at least to my ears. The 500-1.5k region there seems to be a dip, but I'll check that out more over time. The bass is tight, punchy, and sounds great. I wish there was a tad more sparkle to these, but I kind of knew what I was getting. Overall they sound like a great IEM, but I have to get used to them.