Hello Sarmat
Well one thing is for sure, Itil or Atil is the name the Arabs used for the Volga river as well as the name of the Khazar capital on the river. From Arab sources the buildings were all made out of wood because stone wasn't in large quantities and the area was wooded. The last fact makes me dubious about the capital existing on the parched volga delta. It might have been much more to the North than Astrakhan.
I have a wild idea that you might be interested in, those archaologists may be after all looking in the wrong river after all, it may be the Don that is Itil not the Volga but nobody is quite sure.
Al-Jassas