The Layla3g has 8 ins and 8 outs. Actually 16 ins and 16 outs when you, for example, add something like an Alesis AI3..which would then let you do 16 analog I/O from the Layla3g.
You can mistakenly think that the stock Layla3g only has 6 analog ins because you fail to count the 6 in on the back and the 2 additional inputs on the front. Additionally, those two front inputs can handle mic...or line....or instrument. And, the first two channels have available insert points on the back if you want them. And the box is superb with any signal. As is every Echo product ever made.
Why 8 outs? Flexibility. So that one can mix discrete outs to a console if one wants. Or one can route two of the outputs to monitors, and say, two outputs over to that hardware reverb so that it can be integrated into your in-the-box mix...and say, simultaneously send two of the Layla's outputs over to a headphone amp to Eric Clapton who's sitting on the bed overdubbing a real guitar part on your song. Or for simultaneously sending 6 stems out the Layla and over to a Protools HD system for dubbing of stems. Etc Etc.