I second what AirmetTango says. I'm coming up on a year using the ATMax and I usually just turn on the machine in Zero mode and start swinging. Ground balancing is something I normally don't do unless the thing is acting abnormally. GB numbers in my area are usually in a tight range, from 86 to 90. Closer to the Gulf coast or on the beach, I've seen 92-93, but I don't go to the beach often.
That 5x8" coil recommendation is golden. I have 4 coils, but 99.44% of the time, I'm swinging that 5x8". Plenty of depth and easy target pinpointing using the wiggle method. I got 177 coins yesterday and a few pieces of jewelry. Target retrieval is simple and quick.