I e-mailed Marantz Professional tech support this afternoon to find out if/when they will be able to supply a firmware update with the features of PMD661MKII. No response as yet, I'll relay the info if they respond.
I'm basically happy with the unit as it is for what it is, but am looking to switch over to Sound Devices at some point. Yes, 661's and 661MKII's form factor is essentially a desk top/shoulder type design as are so many other manufacturers offerings. It can be an awkward layout but it is workable. If that layout absolutely doesn't work for you they do offer PMD671 which has a different form factor, but they do not offer a model with more tracks.