White's answered the demand for an analog, autotracking unit that would perhaps duplicate the performance of the former 6000 Di Pro SL, but be housed in the smaller, lighter housing like the XLT, Classic SL series and others. Their answer was the very well engineered 6000 Pro XL. It only used about 15-17 parts carried over from the 6000 Di Pro SL, and was designed with a factory preset Target Volume that was slightly higher than the earlier 6000 version, and the Sensitivity was also higher.
The 6000 Pro XL is/was a great unit with the best analog TID display available from anybody!
In 2001, or maybe late 2000, when they brought out the DFX and added the "E-series" title to the XLT, they just changed a few model names.
The Classic IDX became the "IDX Pro" at the bottom of their "PRO" series, and the Quantum XT was renamed the "QXT Pro", and they dropped the long-used '6000' term from the 6000 Pro XL, and then reversed the Pro XL to make it 'fit' with their new "PRO Series. It was renamed the "XL Pro", but only the name was changed. Same circuitry and performance, different name and labeling.
Monte