I am really just looking for the digi-in, is it worth paying the extra money for a nicer and possibly more stable unit with the marantz?
yes, it is worth the few hundred extra for the PMD-661 over the Microtrack II.
from your signature, it looks like you'v ealready got a set of Schoeps, a PSP-3, and a MiniMe.
All that gear is worthless if your recording device freezes or crashes or in some other way loses the recording, because you go home with nothing.
I am likely biased, having had some issues with the original Microtrack, but even so, the Marantz has been a stable, reliable deck - and you don't have to worry about whether or not you'll go home with a recording.