Here is the doubling Map (thanks to SLC for the help) for completing level 3 of each mode (repost):
Prime Directive: Left saucer
Klingon Battle: left ramp
Save the Enterprise: Right ramp
Space Jump: right orbit
Destroy the Drill:Side Ramp
Nero:Left Spinner
The problem is, as KME pointed out in a couple of other threads/posts, you cannot combine the hurry-up 2x combo with the L3 2x shot doubler for 4x (LFS had no problem implementing 4x if the lit snake head and left side double are going at the same time in MET, maybe he can help out the ST team to fix the bug). And the shot doubler is very specific in that it doesn't affect wizard modes, only regular modes. I'm not even sure it affects mb jackpots. When I had it lit on the right ramp and was in L2 Klingon (v1.3 ST pro), it almost seemed like it was only giving me 1x when I tried to combine the 2x combo with it, but I will assume Keith is right in that it at least awards 2x the mode and that I was seeing things.
So for now at least, if you get an L3 shot doubler (as SLC suggests its not really worth going for until the bug fix), I suggest you try and cash it in on L2 and/or L3 modes. It is only lit for the duration of the ball so make sure you have gotten a lot of your L1s out of the way first before finishing one or more L3s as you wouldn't want to drain out on an a relatively small scoring L1 mode and lose the doubler on it.
Hopefully in the next fix the shot doubler will apply to anything lit on the doubled shot including even the combo value.
Quoted from Apollyon:I believe going "3 deep" (not to be confused with going "balls deep"), gets you a playfield doubler. In other words, if you complete all three modes of the same color, you would, for example, double all shots to the left ramp. Complete all three modes of a different color will double a different shot (e.g. right ramp).