How can I print a PDF/X Mavericks document?
Create an Automator print plugin that prints as a PDF-X.

Open Automator.app

Select "Print Plugin" at the Choose a type for your document screen

Select "PDF" from the Actions menu

Drag "Apple Quartz Filter to the PDF Documents" to the workflow space on the right

When prompted choose if you want to create a copy of the original, add or don't add

In the Apply Quartz Filter to PDF Documents workflow, in the Filter dropdown, choose "Create Generic PDFX-3 Document".

Choose File-->Save

Name whatever you like (PDFX)

This will add a workflow back that allows for PDFX again. The workflow is saved in your user directory ~/Library/PDF Services/