Bending Sound

Cool Station To Station reference eh?

I'm needing some guidance on crossovers. I'm planning on adding a set of 2.7 Maggies driven by a set of Reference 250s and the sub that Magnepan recommends:the REL T7X. 

I know that the highest and best use of a set of Maggies is as mid/high speakers and leave the bass work to a sub. Therefore, I need an active crossover that can properly allow 45 to 80Hz at the highest on a 12 or 24db slope that won't contaminate the signal.  Do any of you enthusiasts have some experienced guidance on the best crossover for me?  Thanks!