AR is not known for balanced circuits.
You're mistaken - ARC was building balanced, differential amplifiers and preamplifiers long before the design became popular. The Reference One preamp goes back to the mid-90s, for example.
Phono stage options - balanced with XLR both input and output...
I really like my Elac PPA-2, it's surprisingly good and has bested the few others I've tried. I use XLR/balanced for input and output (for the first time with this one).
It is starting to glitch, and I am considering purchasing another one ('preowned'), but before I do wanted to check here what options you know of in terms of fully balanced phono stages with XLR input and output.