OK I figured out that phono inputs are NOT the same as regular inputs on amplifiers, not sure why I didn't know that before but I used the TRS->RCA cables on a different input and the signal was perfectly clean and the vibrating sound was gone. It seems like the AK1 volume output level doesn't really matter, so i just cranked it all the way up and controlled the overall volume using the Cronus volume knob.
balanced to unbalanced connection
I would like to connect the balanced 1/4" TRS outputs from a Native Instruments AK1 USB audio interface to the unbalanced RCA inputs of a Rogue Audio Cronus. The AK1 is meant to be used with powered studio monitors that have no volume control, so the AK1 has a volume knob that controls the output volume over the 1/4" TRS outputs. These outputs are advertised as being "line level", but I'm not sure I understand the meaning of line level when there is also a volume knob in the equation. I have tried just using a pair of cheap 1/4 TRS -> rca cables that I got from radioshack for testing purposes and found that there was a lot of static and noise with that connection. Any advice on how to proceed with this connection?