Hi Tennrebel, I’m a diehard gpx user, have used for many years as nothing comes close , it’s my go to machine and machine I want to use the most. The gpx’s main issue is: EMi. The 14 inch coil for the 6000 won’t work for your machine, and it’s pretty much a anti- interference coil. Coiltek makes anti interference coils for gpx and so does Detech . I have a 14 inch coiltek and a 11 inch detech . The detech AI can only be found on eBay from Thrace detectors in Bulgaria as the state’s aren’t selling it . The coiltek AI’s are discontinued but still available in limited stock. The AI coils are a different animal. They change tones , high to low , low to high backwards , still sound different even if you invert tones . Pinpoint funny, will make you relearn machine. They still will not have the same depth as stock coils. Best bet is to keep your ultimate 15 on and run in cancel , still will have better depth then most other detectors. I also run a smaller 8 dd detech coil or the Minelab commander elliptical coil, handle emi better , smaller coil platform , less emi. I still pick minnies at 10-11 inches with those coils in crap dirt . Also , run in quiet , lower gains , signal , and stabilizer , noise cancel/ tune in fast motion . Best regards, Antietnam digger