I would read this review.
They go in detail the differences between the Joseph Audio RM25 and the Rm25xl.
http://www.positive-feedback.com/Issue39/joseph_RM25XL.htm
Some of the stuff in the review.
The RM25XL Special Edition sits almost squarely in the middle of Joseph Audio's speaker lineup and, from an evolutionary perspective, represents the third incarnation of the RM25 model (the previous version, the RM25si Signature MkII was reviewed here at Positive Feedback Online by Chip Stern).
The changes to the Joseph Audio RM25XL are all internal and comprise updated drivers and crossovers. While the driver complement remains the same, the actual drivers themselves are all new. The tweeter, built to Joseph Audio's specifications by SEAS, is a 1" Sonatex dual-section dome, a design attribute that heretofore had only appeared in Joseph Audio's top three loudspeakers. With this improved tweeter, Joseph cites improvements in dispersion, which he claims translate into increased airiness and improved image focus. The 7" woofer and 7" mid-woofer that flank the tweeter are still both aluminum and built by SEAS to Joseph Audio's specifications, but differ from earlier versions in possessing 50% larger magnets and 50% larger voice coils, which Jeff Joseph says imbue them with outstanding dynamic capabilities. Indeed, Joseph refers to them as "super-duty" drive units.
In comparing the Joseph Audio RM25XL Special Edition to its predecessor, the RM25si Signature MkII, it was easy to hear the improvements that have gone into the current model. The RM25XL not only had greater extension at both frequency extremes, but resolution in the all-important midrange was subtly improved. Perhaps owing to its expanded dynamic envelope, the RM25XL was more effortless sounding at all volume levels. Lastly, I noticed a greater coherency, with the drive units more effectively speaking as an indistinguishable point-source.