Perhaps an Aesthetix Rhea?
I have a Phasemation EA-350 which has 3 inputs, two of which you can utilize XLR (only in MC mode though) connections. Downside is you cannot change the loading, but does have a mono function and even demag. Pretty rare in USA though...I run every input from a SUT
Have to say that Moonriver 505 has me really intrigued