[Cavet Your Eruptor]

It sounds like latency is what you are describing. I am assuming that by "it sounds slower inside of my headphones" means that there is a delay between when you sing and when you hear it, not that the delay echoes are slower than they should be.

Anyway, the only way I know of to hear it in the headphones right when you sing is to switch ProTools into "Low Latency Monitoring" mode (it's in one of the pull-down menus). I don't know if bus sends still work, but if they do, you should be all set.