Yes, the spell bar file is titled
EQUI_CastSpellWnd.xml. Either delete that from your DuxaUI folder (which will then load the default Titanium client UI cast window), or find another cast window you do like that is compatible with the Titanium client and paste it into your DuxaUI folder, overwriting as necessary.
The default Titanium UI will have a spell bar that looks like the one along the left side here:
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If you don't like that, I know
Savok's VertUI is compatible with P99 and the spell bar will look like the one in the bottom right corner in this picture (note your spell gem icons might be different):
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Just move the EQUI_CastSpellWnd.xml file from the VertUI to the DuxaUI folder and either reload DuxaUI while in game or restart the client.