Hi, I was wondering how the instrument tie lines between EA's studio rooms are wired... seeing as a guitar's output is generally of a very high impedance and unbalanced. Do you use transformer or any active balancing ie. like a DI box sending to a line receiver?

There are two different types of tie lines, speaker and "instrument." The speaker wire is self explanitory, and the instrument lines are low capacitance single conductor w/ shield wires. No passive or active electronics are added. We kepped the runs as short as possible, but yes, it will roll off the high end a bit for cross-wall guitar patching. You can use the output of a pedal as a line driver. We use a noise gate pedal with the threshold turned as low as possible, and that usually works. Some times we will use our DI boxes to lower then raise the impedance.
There isn't a problem with having long speaker run.