Can the SR5 suspension be tuned to be comparable to XREAS?
I'm not aware of anything aftermarket that is similar to XREAS, which crosslinks the shock absorbers. XREAS reduces lean in corners.
The typical upgrades people do to 4Runner suspensions are a lift, which allows them to fit larger tires (thus giving more ground clearance). A lift is going to increase the amount of lean in turns (all other things being equal, which they aren't).
The traditional way to reduce lean is to put on a larger anti-sway bar. I don't know if larger anti-sway bars are available for the 4Runner. A thicker anti-sway bar will reduce articulation offroad. Another approach is to replace the rubber sway bar bushings with solid bushings. Solid bushings are most likely available, but this will also reduce articulation, and give you more things that you need to grease.
If I were you, I'd pony up the money for a Limited. But then I own a 4th gen Limited with XREAS, so I'm biased.