that's a little difficult to follow. By inputs, I'm guessing you actually
mean outputs. ie monitor outputs / headphones outputs )
A headphone amp will
allow you to use more pairs of headphones, but it doesn't change the amout of inputs and
outputs you have in any way. you could send a pair of monitor outputs from the pro 40 to a
headphone amp, and run 4 headphones off it. Is that what your after?