I searched but no one has quite this problem that I'm having. So I got my E7 today and I've had the E9 working perfectly for  a week now and the E7 works perfectly by itself too.
 
The problem is when I dock the E7 in the E9 and try and use them together. The volume is unbelievably low. With both volumes full I can just barely hear the song. I was almost going to ask why there was no sound coming out of it at all until I turned everything way up.
 
I don't know if this even matters but I'm using a pair of DT 990's 600 ohm. The computer is macbook pro.
 
Any help would be greatly appreciated.
 
Thanks in advance.
 
Cillian.

Hi,
 
Do you have anything plugged into the "Line In" jack on the back of the E9? If so, unplug it.
 
Jack

Oh for god's sake... I can't believe that was it..  Thank you so much...
 
I feel like a moron...

@Jack-Micca Sorry to bother you again but what's the optimal way to balance the volume between the E9 and E7? Like leave one full and adjust from the other.
 
Thanks again...

I think it would be the best to have everything at full (so the signal isnt distorted in any way) and then regulate the end volume with ur amp (the e9).

It turns out the volume on the E7 is disabled when docked with the E9. So question null and void... Ha ha... My I.Q. is plummeting today.