No reason they can't be stacked. Here's my $.02 though...ABE's qualities (and there are many) lend themselves better to bulking, Synthagen to cutting/re-comp. I also favor running each solo to better compare/contrast their effects. Gives you a better handle on what's doing what, and saves you some coin.Having said that, the ABE + MPS stack could be explosive. Tempting...
And expensive!