+1 on the 929. It is in the same price range as the X4000, yet you are comparing the older 818 to the X4000.
Since you have Klipsch speakers, I would say the 929 all the way, but you are wanting to drive Maggies in a second zone, which aren't an easy load for receivers. Although the Onkyo 929 may seem to have more power than the SC72(160W vs 130W), when the impedance drops and # of channels go up, the Pioneer looks much much better. There isn't even a proper rating for 4 ohm loads on the Onkyo, just a "dynamic" rating with one channel driven whatever that means nor is there a rating with all channels driven simultaneously. The Pioneer publishes 660W with all channels driven into 8ohms (~90W x7, 1%) and 210W into 4 ohms with BOTH channels driven at clipping. That's a beefy amp section in an HT receiver at that price.
Would I pair the Onkyo with MMG's? No.
Would I pair the Pioneer with MMG's? Probably.
Which has better room EQ? The Onkyo.
Tough choice. If you can maybe get a cheap amp for the MMG's(there is an Emotiva UPA-200 for $150 fs here) and hook it up to the preout on the 929, I think that would be the best compromise.