I don't have Crystal 9 right now, so I'm not sure whether these options are available, but it's worth a shot.
1. Right-click on the subreport and select "Format Subreport". On the Common tab, turn off "Keep Together".
2. Go to the Section Expert and select the section where your subreport is located. Turn off "Keep Together".
The combination of these two should set things up so that the subreport appears directly under the crosstab.
-Dell