Code
<register silent="true" event="equip sub X">input sc group X</register> <register silent="true" event="equip sub Y">input sc group Y</register> <register silent="true" event="equip sub Z">input sc group Z</register>
Alternatively I'm guessing an if statement within spellcast would work, but requires something to trigger the "oh this slot changed!"?
Code
<if EquipSub="x"> <cmd>sc group x</cmd> <elseif EquipSub = "y"> <cmd>sc group y</cmd> </elseif> <else> <cmd>sc group z</cmd> </else> </if>