I could be incorrect here, but I believe that the "H" at the end of 575 refers to a specific model of the Studio Spot 575. It acts as a reference to let you know what features the light contains.
Our
theatre uses six Studio Spot 575 CMYs - they contain booth a
zoom lens and
CMY color mixing. Whereas, the 575H uses two gelled color wheels for mixing color. What other features does the 575H contain or lack? I'm not entirely sure, as I have not had the opportunity to work with that exact model yet.
I hope I could be of some help. If anyone knows more about the difference let me know!