Thanks Art of Sound. I did see that post but it didn't give me a warm feeling about the Zoom.
My bad, I should have posted back after I messed around with this. It turned out that my problem was due to some kind of intermittent connection within the Zoom itself.
I got another one, and it's working fine now as a Mackie Control. It's a little arcane getting it hooked up in Logic (mostly due to inexperience on my part), but so far it seems to be working fine...
If I can spare anyone the frustration/confusion:
Basically:
Download the latest and greatest Zoom R16 driver from their web site and install (I'm using OSX ML and it works fine with Logic Pro X).
Plug in Zoom R16 via USB 2.0 cable, (then on the Zoom itself, select USB, then AUDIO INTERFACE? (Enter), then SETTING? (Enter).
You may need to open Audio/Midi Preferences and set that to the ZOOM R16.
Open Logic and hopefully it sees the Zoom.
Under main Logic Pro X header, select Control Surfaces>Setup
Find and add "Mackie Control" (there are other ones, this one works, can't speak to the rest).
Then (and this is the part that I kept missing) make sure to select the Mackie Control (so it gets a blue box around it) and then make sure the Output Port and Input Port are set to Zoom R16_R24 using the little up/down arrow thingies at the right of each box. I didn't see these/figure out how to select at first... I'm a DA NOOB.
That's it. Open a new multitrack project, assign your inputs to channels, and off you go!
Recording:
All inputs work, level control and faders (which aren't motorized, so it can be a little confusing at first)
Transport and control buttons work, the jog/shuttle is useful.
There are 5 function buttons that by default change the Logic screen setups (can be programmed differently)
Track button seems to mute/unmute only.
The on-board condenser mikes work, if you want them (channels 7 & 8 on the Zoom). Ugh.
Electric guitar direct in seems ok, and a Shure SM57 worked fine. I'll be working with some better mikes hopefully this weekend.
I have it working happily with a late 2011 MBPro, and a late 2012 iMac.
For the money, considering it's a stand-alone 8 track digital recorder (seems to work ok for that purpose so far) as well, it's actually sort of cool. Setup your mixdown in Logic as a wave project, and pull the files off the SD card (Zoom can be configured as a USB card reader easily). Will record at high sample rates allegedly.
I won't be so lazy in future, and I'll report my on-going experience with it.