[Buddha-l] Ts'ao-ch'i or Caoxi?

[Mitchell Ginsberg]

hello all, 
In Chinese Buddhism, there is reference to a mountain stream, in pinyin, the Cao stream (related to Hui Neng, the Sixth Chan Patriarch). The Chinese (if it turns out to be readable here) is 曹溪. What I notice is that when cited in Pinyin this is given as Cáoxī (which corresponds to Wade-Giles Ts'áo-hsī), while when cited in older texts using Wade-Giles, it is almost always Ts'áo-ch'ī (which in pinyin would be Cáoqī). The one exception I find is in the revised Japanese-English Buddhist Dictiontary, where in the entry for Sōtō-shū it is rendered as "Ts'ao-hsi (Sōkei)" although there is no entry at the Japanese word 'Sōkei' itself. 
I notice that 'xi' is a more often found rendering in contemporary Chinese-English dictionaries than 'qi' (at least in the ones I've been able to check). 
What is the explanation for all of this? 
Thank you. 
Mitchell ==========
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