this is normal.. it does this way since long time... when you have a quite full session in dtdm the first time you reopen a song you will get a lot of overload message, just press ok and go forward until the end of the song, the next play will run smoothly. if you want to avoid that do not stress too much cpu, freeze something before save and close.. also remove any kind of anergy saving you have. this is related to dtdm/esb.. but i remember very well a friend of mine on an older mac that has the same problem in core audio, you have to run once your song till the end. so switching back to core audio probably will not solve anything, once you will get busy in core audio you'll have the same problem.