I am waiting for a rebuttal to the sources I linked to. So far all you have done is what you accuse me of doing what you yourself have done.
D.M. DUNLOP, HISTORY OF THE JEWISH KHAZARS (Princeton Univ. Press, 1954): "It only remains now to consider the theory that the modern Jews of eastern Europe, or more particularly those in Poland, are the descendants of the medieval Khazars. This can be dealt with very shortly, because there is LITTLE EVIDENCE which bears directly upon it, and it unavoidably retains the character of a mere assumption. ... To speak of the Jews of eastern Europe as descendants of the Khazars...would be to GO MUCH BEYOND WHAT OUR IMPERFECT RECORDS ALLOW." (pp. 261,263. Emphasis has been added to quotations. Dunlop is a source book for Koestler. Koestler believes the theory that east European Jews are descendants of the Khazars.)
The generally accepted theory is that they are of Turkish origin, But.some have believed that they were ISRAELITES: the "10 lost tribes"!:
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Hasdai, who wrote the Khazar Correspondence, believed they were
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* Isaac ‘Akrish, who first published the Khazar Correspondence, believed the same
* Karaite Jews of Crimea (once part of Khazaria) and Poland "claim a connection" with Khazars.....Karaite Jews claim to be directly descended from New Testament Saducees, Jews who reject the Talmud (some Russian governments would exempt Karaites from Jewish persecution, considering them to be the "10 lost tribes," and therefore not responsible for Jesus’ death)
Ibn Fadlan, an Arab writer, refers to the Khazar king as "a Jew"
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Maquadasisi, another Arab, says, "in Khazaria...Jews exist in large quantity"
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Inb Hawkal, Arab, says only a Jew could be a Khazar king
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Masudi, another Arab says the same
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In Russian folklore Khazaria is referred to as the ‘country of the Jews’
Here is another source that does not totally support your "primary source".
http://www.reference.com/browse/wiki/Khazars
You keep referring to King Joseph as if his ancestory determines the ancestory of all the inhabitants of his kingdom. Appealing to just one man does not make all who lived in his kingdom descendants from Japheth. This is like assuming that since the House of Windsor is actually German and not English all Englishmen are in fact Germans, or that since Queen Elizabeth II is head of the Church of England that all Englishmen are members of that church.
Also, although you reject the conclusions of genetics and DNA, I do not.