Are you using the amp as a SPEAKER or as a MONITOR? Does your PA already have the 2 black rectangles with spongy material in front connected to it?
A MONITOR (or more aptly, stage monitor) is for individual instrument players and vocalists to hear themselves on stage. These monitors can be amps and would be connected to your parallel output of your DI. In the case of vocal or drum monitors, these would be connected to the AUX output of your mixer.
If you're trying to use your bass amp as a SPEAKER, don't.