To get more tracks (assuming mic level) than with a 788T, you'll need two 8ch preamps, one of them outputting AES. This narrows down the choice a bit.
You need to power the preamps as well. And then you need to hook them up to the PIX's inputs. Lots of cabling, lots of possible failure sources.
So I don't think it's a good solution for "really portable" like in a bag. It may well work in "remote recording" of concerts, where others would use the same 8ch pres but feed them into a computer interface or an HD24
Remember that the other 16 inputs are through the video inputs. HDSDI and HDMI. I don't know of any mic pre that has HDSDI or HDMI outpus.
If it's to be really portable, I'd rather link two 788Ts if I need 16 mic inputs.