I wouldn't worry about gain staging or the Y cable on your setup.

Gain staging is important on the bigger L1 Bose. I means that you adjust the signal level of the output before it reaches the main volume control. As long as your KN volume is up, you are alright.

The Y adaptor is used by some to combine the left and right to mono, which the Bose is. In my experience with the KN7000, the Mono jack is all that's needed for full fidelity.

Bernie