Why are amplifier transformers sized the way they

Sean, I have a quick question for you, if you don't mind. I need to buy a sub panel box. I am confused as to which brand/model/features that I should look for. My current thought is just about any that has a solid copper bus. Is there anything else I should know? Thanks, Brooks

Sean, thanks. The electrician that I spoke with said the only thing that I needed to be concerned with is having enough slots.

I read a comment of yours in another thread about keeping all breakers on the same phase. Does this apply to the sub panel or just if you are running the wires from the main box? If is applys to the sub pajel, then it would seem that I would need a box with twice as many slots as I need because every other one would be unused. Thanks for all your time and advice.