Hi hybrid,
As JohnK pointed out, you can simply get an unbalanced-to-balanced adaptor, which will let you use your RCA unbalanced connectors to the Crown amp.
What you are referring to as "volume controls" on the front of the Crown are likely input level controls. Using these, you can reduce the intensity (amplitude) of the incoming signals so they don't overload the input section of the Crown amplifier. You'd only need to use those if you were using a line-level source with unusually high output.
Typically, you'd set the Crown input level controls to maximum and use your preamp volume control to set the overall level.
Regards,
Alan
