suggest receivers for magnepan MMG or MMGW HT

IMHO, no. Sorry.

Pop on over to the Planar Asylum. People have had success with the Outlaw products.

I read others recommend Aragon or Arcam (I want to eventually get the Magnepan HT system - MMGC/MMGW - and am thinking about using an Arcam AVR300 with them).

You can get away with a lower powered, higher quality receiver like B&K if you use killer subs. Set the crossover higher (120hz?) and it will help greatly with the demand on the receiver.
However, if you haven't tried the maggies already, beware. They sound great but have a very narrow "sweet spot" 1, maybe 2 people cuddling, will have good sound. Anywhere else in the room will sound like you are in the hallway listening.

Onkyo recievers will power a 4 ohm load