Broadly speaking, when a computer gets very warm under load, this is an indication that it is *working correctly* and discharging the heat buildup. For some reason, people just refuse to believe that Apple actually considered this in the design of the computer. Always boggles my mind a little.
If the computer was actually *overheating,* it would shut down to protect the processor. If that's not happening, it's not overheating.
When the computer seems to be working far harder than it should to handle what's going on (Pro Tools = pretty demanding application), it's usually down to three issues:
1. The computer is underpowered for what you're trying to accomplish. Fix: buy a more powerful computer.
2. Computer is having to write to disk way more than it should. Solution: buy more RAM.
3. Computer is not efficiently discharging heat and must work harder than it otherwise would. Solution: clean out the dust from the fans and ventilation systems.