Then there is Toro also using the same engine in their Groundsmaster mowers and Workman Utility so that could also factor on the switch. Keeping a 23 horsepower rating may have been under the requirement. I seem to recall that ROPS began to be required around this time period.
Another reason could be a change in regulations, here or in Europe, regarding horsepower. Regarding the switch, it could be that the DM850D was less stressed for the application with less cubic inches and/or cheaper so it began to be substituted. The 523Dxi was originally developed for the European market and then also sold here in the USA.
