I have a follow up question to my recording from the direct outs, of a house mixer, to my mixer--to interface. Once the inputs on my Yamaha mixer are full , and input 1 & 2 of my Scarlett 8i6 are used (L&R out from the Yamaha), I still have inputs 3&4 in the back (line inputs only). Apparently the only input gain control on these is to choose a low or high gain setting via Scarlett Mix Control. So which would be better? I assume that it is going to depend on what that line is attached to???.... need coaching.
 
Thanks !

Yup, depends what you're plugging in there. As a general rule, use the lowest gain setting that works. If you're plugging in a hot line-level signal such as a synthesizer output, turn the synth up and the input channel down. However, the only way you're going to be able to plug a microphone in is by adding a preamp. If I were in your position, I'd look at getting a small second mixer.