The Marantz has much finer resolution (0.1 ft) for distance and also Audyssey XT32 with individual dual sub support and ability to tweak the curves. You can also turn off correction for the mains. I think it supports a newer HDMI standard too. I like the internal layout much better and I expect with HDAM and current feedback, the Marantz would give better imaging and soundstage than the Onk.

Refurbished sucks a bit but you have 90 days.

House of the Rising Sone
Out in the mid or far field
Dedicated mid-woofers are over-rated