Phonetics Question

Hi,
i've been working recently on figuring out some sound-shifts between the
different stages of Rokbeigalmki:
Ancient >> Old (Present) >> Modern (Future)

"Old" Rokbeigalmki is the main form of the language that i work on.
So, i figured out an idea that Ancient Rokb. would have consonants that
were more "backed" in the mouth, and less true fricatives.
So, for instance,

( "<<<<"  means "comes from")

present {dh} /D/ <<<< dental (NON-alveolar) voiced plosive
present {k} /k/ velar <<<< /q/ uvular unvoiced plosive
present {kh} /x/ <<<< /k/
present {f} /P/ bilabial <<<< /f/ labiodental

So, i hope that gets the idea across....so, i've been wondering.

I want the the Ancient forms of _s_, _z_, _sh_ (/S/), _zh_/_jh_ (/Z/),
_tz_ (/ts/), _ch_ (/tS/), and _j_ (/dZ/) to be based on what i think is
the Chinese {x} sound, where (if i'm pronouncing it correctly) the tip of
the tounge is lowered below the level of the lower teeth, 'humping up'
the main part of the tongue closer to the palate than it would be for a
normal sibilant.

What is this Chinese {x} sound, phonetically?  Does it have an IPA
symbol?

Thanks,

-Stephen (Steg)

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