Now that we have a E-V13 of obvious European (Paleobalkanic) origin in ancient Central Asian Steppes we can speculate on similarities of the name of Dacians and Iranian Dahae and off course the Diau / Tao in ancient Armenia.

Now that we have a E-V13 of obvious European (Paleobalkanic) origin in ancient Central Asian Steppes we can speculate on similarities of the name of Dacians and Iranian Dahae and off course the Diau / Tao in ancient Armenia.

What is the direction? From Iranian to Balkanian or the inverse? Or maybe chance similarity? Or common origin?

Furthermore I think the transformation of Daoi into Dakoi can be simply explained by the -k' plural suffix present in Armenian and possibly in some Balkanic languages.

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According to Strabo's Geographica, the original name of the Dacians was Δάοι "Daoi".[2][22] The name Daoi (one of the ancient Geto-Dacian tribes) was certainly adopted by foreign observers to designate all the inhabitants of the countries north of Danube that had not yet been conquered by Greece or Rome.[12][12]

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The ethnographic name Daci is found under various forms within ancient sources. Greeks used the forms Δάκοι "Dakoi" (Strabo, Dio Cassius, and Dioscorides) and Δάοι "Daoi" (singular Daos).[23][2][24][a][25][22] The form Δάοι "Daoi" was frequently used according to Stephan of Byzantium.[17]

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There are similarities between the ethnonyms of the Dacians and those of Dahae (Greek Δάσαι Δάοι, Δάαι, Δαι, Δάσαι Dáoi, Dáai, Dai, Dasai; Latin Dahae, Daci), an Indo-European people located east of the Caspian Sea, until the 1st millennium BC. Scholars have suggested that there were links between the two peoples since ancient times.[30][31][32][17] The historian David Gordon White has, moreover, stated that the "Dacians ... appear to be related to the Dahae".[33] (Likewise White and other scholars also believe that the names Dacii and Dahae may also have a shared etymology – see the section following for further details.)

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Opinions on the origins of the name Daci are divided. Some scholars consider it to originate in the Indo-European *dha-k-, with the stem *dhe- "to put, to place", while others think that the name Daci originates in *daca – "knife, dagger" or in a word similar to dáos, meaning "wolf" in the related language of the Phrygians.[38][39]

One hypothesis is that the name Getae originates in the Indo-European *guet- 'to utter, to talk'.[40][38] Another hypothesis is that "Getae" and "Daci" are Iranian names of two Iranian-speaking Scythian groups that had been assimilated into the larger Thracian-speaking population of the later "Dacia".[41][42] 

https://en.m.wikipedia.org/wiki/Dacians