2 heads 1 stero cab

Thanks for the answer. 

I would like to A / B / Y them if that's possible?

The ultimate cheap Bonamassa rig with 1 cab.

All you need is an aby switch. I recommend one with at least ground lifts in it like the palmer or voodoo. I know they are capable of handling more than two amps, but they won't suck your tone. If you find that you set up lacks bass and kinda sounds like a bad phaser pedal (as joe says) you are probably out of phase. To remedy this you can do three things: 1) connect one of the heads to the cab with a speaker cable wired in reverse on one side; 2) switch the speaker leads on one of the verticle sides of the cab (both speakers, this requires opening up the cab); or 3) some of the aby switchers come with phase switches like the palmer. The voodoo may also.

Caution: don't use the three to two prong adapters that you put on the power cord to remedy a ground loop. Some people do it, but it is very dangerous if you don't know what you are doing (and even if you do know what you are doing). As a rule of thumb, don't disconnect the amps saftey earth ground.