Zd542: the Pass XVR-1 takes care of two birds with one stone: (1) the Linn Akurate 212 is a monitor, and the XO splits the signal (I have it set at 78 Hz, 18 db slope) to relieve the monitors of bass duty, and the JL F112 handles all the low stuff; and importantly, (2) resolves (completely) an otherwise serious impedance mismatch between the Act2.2 and the MC452. This XO is capable of literally thousands of different cross over configurations, but each micro adjustment requires one to remove the hood and manually switch the jumpers on the circuit board, and it takes a lot of trial and error to find just the right setting to one's liking. It is not for the squeamish. I am squeamish, and Pass was great guiding me through the month-long process (am less squeamish now).
Thanks all for Mc/Act input so far. Would appreciate others' thoughts as well.