x: Move upward and forward the front part of your tongue surface and make it approach the front hard palate, with a narrow chink left; pronounce with the breath squeezing out from the chink. s: Stretch forward the tip of your tongue and make it approach the back of the upper teeth, with a narrow chink left; pronounce with the breath squeezing out from the chink.

i don't really understand ur question, but x is an initial, its pronounciation doen't change, the difference depends on the finals combine with it. x can combine with these finals: xi xia xie xiao xiu xian xin xiang xing

x vs s? please send me your email by the italki online message and i'll mail you my pronunciation.

resemble the pronounciation of "ch" in Deutsch.

differect to explain. now try to this way： first，when you pron“ ∫”，your tongue backward，sound from there then put your tongue forward，the sound at mid tongue“x”pron； or this way： when pron”s”your tip tongue to the root of front teeth，next roll a little your tip tongue to pron “x” try to do ，if you still can pron well，i will find another explain. upward