I think this may become a FAQ and also useful as some people won't know and thus benefit from this excellent addition to MFME.
A new feature with v6.0 enables you to link the top box and slaves together, so you just click to open the top box of a machine and it will load in all the slaves and position them correctly.
But first you need to link the top box and slaves together, here's how.
1/ If you already know how to open up them all individually then do that first, using v6, by using the same method as you would have opened them in v5.1 (game manager users, can now right click on the slaves and open up a new instance)
2/ With them open, make sure you position everything on screen where you want, so i.e. position the slaves correct, remove the file menu, by pressing f1 on each individual slave. If you need to reposition then press esc and adjust.
3/ With everything positioned correct and the file menu not showing on any of the slaves etc, click on the top box, so it is now in focus.
4/ Now push alt L and you will see it say thats the top box and slaves are now linked.
5/ Press ctrl q and it will close everything down, save layout if it asks.
6/ Now when you open the top box for the machine, all the slaves will open and everything will be positioned where you want it and no file menu showing (if that's what you want). i.e you no longer manually need to open up multiple instances of MFME and the slaves individually.