ground plane interference with output

[mazurek]

People have warned me before to isolate the input buffer from any ground plane, I was wondering also if the output needs to be isolated. My specific application is an active crossover, going three inches of balanced line to the driver on a UCD amp module. The ucd module input isolating op amps are disabled, and the input signal is connected directly to the modulator, in order to run my crossovers at higher gain, and get rid of the UCD highpass pole.

I actually can save some money and weight if I print 4 layer crossover boards because of reduced surface area and chassis size. Free Eagle, doesn't allow me to make a big enough board, so I use ExpressPCB. They let me make power/gnd planes, but don't allow any keep away regions on the inner planes, so the output op amp would be close to the ground plane.

Thanks for any answers.
Lee