First of all, let's just clarify something: the "balanced cables" you're talking about are not normal balanced cables. You can either use an isolation transformer and connect a mono cable from the amp to the transformer and use a balanced cable from the transformer to the G System, or you can use what's called a pseudo-balanced cable (which is a normal balanced cable with a stereo plug at one end but a mono plug at the other end, where the shield is cut and not soldered and the "cold" wire is wired to the plug's ground where the shield would normally go) from the amp to the G System (the mono plug is used for the amp and the stereo plug for the G System).
Next, it'd be useful to know whether you're running your G System's brain mounted in the pedalboard (away from the amp) or rackmounted (close to the amp). Anyhow, if you're running the whole G System through the loop, you won't benefit much from pseudo-balanced cables. However, if you're running your G System in 4 cable method, you may find the pseudo-balanced cables help to reduce hum. I use all mono cables except from the G System's Insert Send to the amp's input, where I use a pseudo-balanced cable.
Hope that helps!