So here is the flow of my setup at the moment,
MacBook Pro -> Aune X1S -> Little Dot MKII -> Aune X7S -> Sennheiser HD660S
So the issue that I am having is that when the volume on my laptop/iTunes is at full volume the sound begins popping very badly and sounds like there is a lot of static. I did not have this issue before adding the Little Dot into the mix. Previously when I had just the X1S and X7S I had the volume on my laptop at max with no issues and just controlled the volume with the X7S. Is it normal for that to happen or is there something wrong with my Little Dot or the tubes in it? Will it go away with time as the tubes "break in"?
No that is not normal. Tubes would be the first guess but that it is on both sides (you didn’t say but I’m guessing it is) that would tend to be something else maybe. Cables is also something to look at as trying different usb and rca’s . Another thing I would try is not plugging the X7S in to the LD. On my Yggy it has the outs two rca’s And a balanced and if I have my tube amp into the rca and Liquid Carbon on balanced the sound is very distorted if the Liquid Carbon is not turned on if it is powered up all is good if I turn it off sound is distorted. Try unplugging everything and go one at a time and see if it changes .