3gx location

[mrnurse]

I have just bought my first heli, a tree 550e v2. My question is where should I mount my 3gx unit? I prefer the idea of it going above the tail unit on the little platform but other forums say that this can lead to vibration in some cases. I feel placing it under the tail unit between the side frames would be restrictive for setup, binding etc.
also, I am using a spectrum dx6i. Can I just connect 2 spectrum satellites to the 3gx or do I need to use my ar8000 as well?
thanks in advance folks
paul