I would look at alternatives to the M2's Crown amps if you already have M2's. The best I've heard of is using a Motu Ultralite MK V multichannel DAC/USB interface ($600), 4 channels of Hypex MP502 such as Buckeye Amps ($1200), and having Mitch Barnett (accuratesound.ca) at take your measurements and design FIR's using Audiolense ($600). The FIR's can then be run in Roon if you have it. No need at all for JBL's XO's implemented in the Crowns and sounds fantastic. Subs can (and should) be integrated too, which the Motu accommodates.
