This can be attributed to your playback engines buffer settings. If you INCREASE your playback buffer size, you should have better luck with more processes at one time. If you DECREASE your buffer, you will have improved monitoring latency. It may be common to decrease for tracking and increase for playback and editing.
Additionally you could:
Make sure your audio program is the only thing hogging CPU. Turn of other Programs.
Record on an external harddrive.
Defragment your harddrives.
Amongst other things that arent flowing off the top of my head!
Hope that helps solve your problem. Good luck, Eric.