I was just about to ask the same thing, having just upgraded from a 6000/Di Pro SL (circa 1992) to an XL Pro myself. The reason for the upgrade is that I loved my old Di so much I wanted a new one that was lighter and could share the batteries with my XLT. After using the XL Pro for the last few days, I don't know why I ever bothered to go from the Di to the XLT (but that's a topic for a different post). The Di and the XL seem to operate identically as far as I can tell. Yes, I'd heard that the XL has a totally redesigned board using surface mount components, suposedly making it quieter, but honestly I can't tell the difference. Since there was a near total redesign, evidently, I'm surprised there isn't a perceptible difference in operation. They both operate just wonderfully. The XL Pro is in my mind the ideal detector for the coinshooting I do, but mainly just because it combines the wonderful oeration of the Di with the modern ergonomics and batteries of the XLT/DFX/etc.. Now the question is what to do with my old SL; sell it or keep it as a backup to my backup (my XLT has now been relegated to backup status to my XL Pro). ...gotta say, I just love these analog machines.