blending Magnepan MMG with SVS subwoofer

I'd start by measuring the response curve of the MMGs in your room. You can get fancy tools for this or use a free app like Octave RTA on a tablet, put the tablet in your listening position and run a frequency sweep to see where the MMGs start to fall off. 

Then set the low pass on the sub to match and dial it in from there by ear. 

Why do you have the sub on the side wall? Even if you achieve flat frequency integration the wave front is going to be seriously out of sync, and you may have nodes in the room that you can't solve through adjusting the power and frequency of the amp.

I would center the sub between the left and right channels to start. Room nuances will dictate final positioning. 

I have the 1.7s and went from one sealed sub to two ported subs and finally am now using two open baffle subs (home brew). Having a dipole that couples to the room similarly to the panel was a revelation. Also, for me, trading excursion for surface area was the largest step forward in musicality of the lowest registers. 

I don't know how much of an analog the 1.7s are to the MMG, but my subs are crossed fairly low, 88hz. 

I've successfully integrated MMGs with both Rythmik and Velodyne subs using Audyssey.  It's amazingly effective and virtually idiot-proof, but I understand that it's not everyone's philosophical cup of tea.  If that doesn't appeal to you, I'd suggest that you try to find a Velodyne SMS-1 sub controller.  (They were roughly $400 new, so hopefully you can find a used one that's not too expensive.).  This is a much more cumbersome set-up procedure than is Audyssey, but - once dialed in - it works extremely well.  It will take some time, but IME - if you invest that time - you will very likely get essentially perfect integration from an SMS-1.

bgoeller--Right you are! OB/Dipole is the ultimate sub for use with planar speakers. Anyone seriously interested can read about a particularly good one (featuring the Rythmik Direct Servo feedback system and dedicated 12" woofers used in opposing pairs) can read all about it on the Audiocircle GR Research Forum.