1) Guitar > Amp > HEIL > cabinet - This scenario is best if you only have one amp obviously. I didnt like it when I ran it with my Marshall Combo. In order to get the volume through the Talkbox loud enough to be used, I had to crank the amp, but then when the talkbox was off, it was insane stage volume...so that was a no win. Also that will give you just straight amp or talkbox
2) Guitar > A/B -A) Amp > Cabinet, B) 2nd amp > Heil Talkbox - This is the setup I have been using the most. That way I dont have to worry about my original sound mixing with the talkbox and diminishing the effectiveness of the effect. I'm sure you can mix the two, but the soundguys we have had when I've wanted to use it, barely seemed to know how a mixing board worked. Much less blend two guitar sounds and such. I would just simply leave the talkbox on the whole time, and when needed I would switch from A to B. If you sing, a separate vocal mic is usually good too.