Hmmm, first listen with the Vega confirms my impressions that it would not be the best match (for my taste). I actually had to turn down the volume to half what I use with amp1 as the bass and lower mids were overpowering, and the single ended output of amp 1 is roughly equal to amp 2. I have not heard the Tia Fourte but from trusted comparisons I gather Tia is airier and overall more balanced even if it's still also a colored presentation (like a much refined U12 with treble sparkle).
Next will be trying out the Elear but as it shares some of the Vega's aspects not sure about it (given what I have read on the Utopia vs Elear, not surprised amp2 would be a good match).
As usual our perception regarding U12 vs Vega differ, but Vega is so polarizing (love it or hate it) with its unique (bold?) tuning. Yes, Vega is not airy or doesn"t have the biggest soundstage but that can improve quite a bit and DX200 with amp1 is very good in that respect the Vega "breathe" and find a bit more balance (all of this, with balanced output). On the upside, nothing I have heard beats Vega's physicality (the Elear does a pretty good job of being an "open back brother" of sorts there, except bass is less overpowering than Vega and treble have less sparkle). Vega bass are tremendous but I wouldn't say they overpower the mids when properly powered.
I don't know about Tia, it sure is not in the same price range
I am wary of "same league" stuff, each IEM has a strong suit and some like Vega have a singular (unique?) tuning which makes comparisons tricky... but Tia is one of a kind technologically that's for sure.
But back to amp2 : it's amazingly musical, I just love it!