The final 5900 Di Pro SL and 6000 Di Pro SL models each used the same 'CB" (Composite Board) circuitry an the only main difference was manual GB Vs Auto-Trac GB.
These detectors were housed in the larger-size control housings and the were powered by 4-C cell batteries.
The 6000 Pro XL was later renamed simply the XL Pro (when they changed several model to a "Pro" series). The 6000 Pro XL was White's efforts to retain the excellent 4-filter type performance an the even better needle meter display, but in a smaller-size housing. They used the same control housing as the XLT and powered by the 8-AA slide-in battery tray. The 6000 Di Pro was not down-sizeable so some engineers designed a replacement model, and they named it the 6000 Pro XL. I was told they only retained about 15 to 17 parts from the 6000 Di Pr SL, and they eliminated some adjustments, peaked the Target Volume a little higher than the 6000 Di Pro SL could be set, and they also enhanced the Sensitivity a little to boot.
The 6000 Pro XL and renamed XL Pro gave us a lighter-weigh detector, a better balanced detector, let us use the cheaper and lighter, fuel-efficient 8-AA batteries, and I sure wish White's would have been able to keep the XLPro in their line-up. I also have the XL Pro (or 6000 Pro XL,if that's all I can find) on my Want List, They can easily hold their own against most (or all) of the top-end detectors on the market today as all-around versalite detectors.
Monte