[xsl] Testing condition on external XML

I am transforming data from a database into an XML format. I want to run 
the transformation only on a subset of all records I have available. I 
put identifiers for those records that I want to transform in a simple 
external XML file, which I would like to use as filter.
Only those records should be transformed where 
document(acquisition-nums.xml)//acqnum matches 
tuple/atom[(_at_)name='ObjAccessionNo'].
The way I constructed the test does not work and the whole set from the 
source file is transformed. I got stuck on this and can't move further. 
I appreciate any hint or help on this. I am using Saxon B 9.1.0.7.
Thanks in advance, Standa

Here are the file samples:

File 1 - Source File (records.xml)

<table name="ecatalogue">
  <tuple>
    <atom name="ObjAccessionNo">2009.030</atom>
    <atom name="ObjTitle">OBJECT TTTLE</atom>
    <atom name="DatDateCreated">2009</atom>
  </tuple>
<tuple>
    <atom name="ObjAccessionNo">2009.031</atom>
    <atom name="ObjTitle">OBJECT TTTLE</atom>
    <atom name="DatDateCreated">2009</atom>
  </tuple>
</table>

File 2 External File (acquisition-nums.xml)

<items>
  <acqnum>2004.045</acqnum>
  <acqnum>2005.098</acqnum>
  <acqnum>2008.007</acqnum>
  <acqnum>2009.030</acqnum>
</items>


Stylesheet

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"; 
version="2.0">
  <xsl:output method="xml" encoding="UTF-8" indent="yes" name="xml"/>
  <xsl:variable name="acq-num" select="document('acquisition-nums.xml')"/>

  <xsl:template match="table[(_at_)name='ecatalogue']">
    <collection>
      <xsl:if 
test="tuple/atom[(_at_)name='ObjAccessionNo']=$acq-num/items/acqnum">
      <xsl:apply-templates select="tuple"/>
      </xsl:if>
    </collection>
    </xsl:template>

  <xsl:template match="tuple">
     <record>
       <identifier>
          <xsl:value-of select="atom[(_at_)name='ObjAccessionNo']"/>
        </identifier>
      <title>
        <xsl:value-of select="atom[(_at_)name='ObjTitle']"/>
       </title>
        </record>
    </xsl:template>

    </xsl:stylesheet>




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