Print PDF in duplex mode

Hi
I have a PDF document that is stored in the iSeries' IFS folder and want to print it using Java that is running in the iSeries' JVM. Just printing the PDF and sending it to the outqueue works perfectly fine but now I want to to print it in Duplex mode using

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String outqueueName = "/QSYS.LIB/QUSRSYS.LIB/" + outqueue + ".OUTQ";
OutputQueue outputQueue = new OutputQueue(as400, outqueueName);
parms.setParameter(PrintObject.ATTR_OUTPUT_QUEUE, outputQueue.getPath());
parms.setParameter(PrintObject.ATTR_HOLD, hold ? "*YES" : "*NO");
parms.setParameter(PrintObject.ATTR_SAVE, save ? "*YES" : "*NO");
parms.setParameter(PrintObject.ATTR_SPOOLFILE, ""); parms.setParameter(PrintObject.ATTR_DUPLEX, "*YES");

SpooledFileOutputStream outputStream = new SpooledFileOutputStream(as400, parms, null, null);
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but it still just prints single page mode.
Does anyone have an idea what I am missing here?

Max
--
"The best laid schemes o' mice an' men gang aft aglay."
Robert Burns