creating filter routes (howto?)

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I've constructed a two filters and defined what I believe are proper 
route records in mime.convs, foo.convs, mime.types, foo.types and 
foo.ppd. Upon restart CUPS loads my filters. When I send an IPP job CUPS 
correctly detects the desired type from foo.types and starts my first 
filter. That filter accepts the job, filters it and passes its results 
to (what it thinks is) stdout. According to my convs/types records CUPS 
should then *should* route the job off to either pdftops or a pstofoo 
filter I wrote yet CUPS does nothing.

The files are quite simple being PDF or PS files with a header attached. 
The first filter simply removes the header and hands a %PDF or 
%!PS-Adobe stream to stdout. It's expected that CUPS will then route 
%PDF through pdftops and then my custom pstofoo filter *or*, if the 
content from the initial filter is PostScript CUPS should route directly 
to my pstofoo filter. I've disabled all of the standard mime.convs 
filters except pdftops in an attempt to get it to work but CUPS still 
refused to route the job beyond a single filter.

Any ideas on what I've done wrong?
Is there a chapter or content in MS's book that I missed?

Thanks,
JR