Thanks. The 9300 and 9600 use almost the same firmware, they are both based on Montavista 3.3.1 and use busybox as their shell and for the usual Unix tools.

If anyone wants to try enabling prontoscript in the TSU 9300 with 7.3.3, setting

APPLI_ARGS="-E prontoscript"

in /run.sh in the optfs may be sufficient. Surprisingly, the Appli binary that contains the actual Pronto software is 1.2MB on the 9300 and only 0.8MB on the 9600.