WHE dont know *****.
The difference in price between S type fitting and Elinchrom fitting is vastly inflated by people who should know better.
They are almost always the same if comparing a quality brand like genuine Bowens to genuine Elinchrom modifiers. Some excellent modifiers are only available in Eli, like deep throat octas and the original reverse fit Octabox, though I now see Bowens are offering reverse fitting on their octas.
And if you want third party, there is no difference.
Compare the prices here:
http://www.bessel.co.uk/acatalog/Soft_Boxes.html
Look on Ebay for plenty of Eli fit modifiers at equally cheap prices.
The D Lite is an excellent first choice, btw.