I got mine last summer used like you, and I am really only beginning to understand what things do now. I don't have a problem with quarters, in fact running the stock coil I can tell if it is a quarter just by the sound it makes. I am usually running a stock program, or one that is slightly modified for my location. Check the discrimination for your program, gold can ring up in the low negative VDI scale. As previously stated try the 15khz frequency for gold.
There are plenty of very experienced DFX users here who can probably help you out more than I can.
The digging deeper book by Jeff Foster is a must for understanding what all the settings do.
Good Luck and HH