I sense a bit of discrepancy here with "just not enough for me (killing my low back)." vs. "The "racier" the better in terms of geometry".
How do you define racy, is it stack, reach, responsiveness....?
Anyway: you will have western brand choices, the Canyon Endurace was mentioned already but there are certainly other choices for taller riders with even more stack.
Highest stack options for Chinese road bike frames that I am aware of are are Yishun R068-D (not sure they still do B2C), Hongfu FM238, Carbonda CFR-505 SL (XL might not be available) or Elilee Blize (not exactly "low cost").
However, none of these options has significantly more stack than your existing Aeroad in 2XL.
It seems odd, as slammed stems are the norm but you might need to consider working with spacers?
Racy - a combination of things: Geometry - placing the rider more over top the bottom bracket, stiffness/responsiveness - will the bike respond well to high power (1600W+), aero tubing - does the bike slice through air.
Even though my Aeroad 2XL has a "tall" stack compared to most, because of my overall height the drop from saddle to bars is 130mm, which I hoped I could handle but I think over time it's compounding into low back discomfort.
I've maxed out the spacers under the cockpit so no more options there.
I know I'm looking for a unicorn bike that actually just doesn't exist (why would a manufacturer make a 660mm stack, aero race bike for the 6 people in the world that want that geometry). Although - the Pinarello X's are pretty close for a "racy" aero bike - I just don't have a spare $25,000 lying around for that bike (and used bikes or frames in that size are not available).
I'd actually be pretty happy with the modern Endurace - it's a great bike by all accounts and does fit the bill for what I'm looking for. Was just hoping there's a Chinese frame out there in a similar size as I have a great gruppo and wheelset on my current bike. Would be $1500 vs $8000.
Appreciate those options! There are just so many Chinese makers and models out there now it's hard to know if I haven't missed anything.
Cheers,
Jesse