Your only options for pulse delay adjustments are with the timings.... and being an experienced user of the GPX series detectors I see no reason why you would want to run one without the ground balance turned on. Its an easy thing to try though, just simply turn it off and see if its stable. If not, turn it back on and resume hunting. Note that as a general rule the GPX series machines are a bit deeper than the TDI anyway....
If you are able to make it work though, no doubt a bunch of us would love to hear your experience with it!