[NTG-context] PDF v1.6 inclusion

Hi. I'm trying to include some PDF files generated by Acrobat 7, which means they are PDF v1.6. ConTeXt (recent distribution, on linux) complains that "PDF version 1.6: Xpdf only supports 1.5". I thought that maybe I could switch to using Ghostscript instead of Xpdf-tools to process the files, in the hope that ghostscript would support 1.6, but I'm stymied trying to pass the correct parameter via texexec. Am I on the right track, and if so, what should I type? Many thanks, Duncan