ID is not known to be good at direct printing and the normal workaround is to export PDF and print that. Waht settings have you been using to export the n-up file to PDF? Is the link listed as up to date?
Peter has made mention of his preference to export from ID and print from Acrobat. I have read this advice numerous times, but cannot support it.
I can offer that, upon his advice, I long ago set all my print settings to include, from the Graphics Tab - Send Data > All.
(I have gotton away from using ID for imposing. We print to a Bizhub with a Fiery Graphics Arts package)
InDesign strong points - With the scripts you can accomplish quite a bit.
Acrobat - if you ever toggled - Advanced > Print as Image, that setting stuck and all subsequent printing has been based upon it's defualt 300 dpi, no vector. Quite Imposing is a plugin for Acrobat which handles most of the imposition you might need.
Your Xerox may have simple to advanced imposition bundled as part of the RIP package.
I'll add to this and say that I support Peter's statement 100%.
I never print directly from InDesign.
Thanks for the input so far everyone. Nothing I do seems to work... Our Xerox has an integrated fiery unit as well, for what that's worth. Our usual export settings to PDF are the standard "High Quality Print" package. I've also tried modifying these using different combinations under the output -----> color tab but to no avail.
I also always use the (send data ---> all) setting as a standard. It has not affected this at all.
So far most of my printers have behaved with ID, so I can go either way, and I'll do intermediate samples direct from ID quite often, but I pretty much never do actual final output from .indd files if for no other reason than the PDF seems to always process and print more quickly, perhaps because the images are properly optimized (as you noted, optimized subsampling in the Print dialog is a disaster in ID), and of course if I'm proofing something that goes out to be printed professionally I always proof from the file I'm sending, which is the PDF.
So you get PDFs from this client, and they print OK when rasterized in Photoshop, but not otherwise. Is there any consistency to this, i.e. is all PDFs form this client, and only the ones from this client? Are all of these PDFs produced the same way by the client? How?