Sync issue using Mbox 3

I am using some professional animation software (TVPaint) and I came to notice that when I use the Mbox 3 for sound output instead of my iMac's built in sound, the sound plays about half a second late, which is terrible. When I switch back to the internal sound, it plays perfectly in sync. Thing is, this only happens with TVPaint, but given that it plays perfectly when using the iMac's built in sound, the software support would tell me it's to do with the Mbox and not them. I wonder if anyone has any idea why the Mbox 3 would cause this major issue with this one application. It means I have to switch outputs when using it.