Systems of eight tones are very much local matters. The Byzantine Tone system is not used uniformly throughout even what was the territory of the Empire, but certainly has currency at Constantinople. There are more modern and Western-sounding tone systems in common usage in Greece, where the exact melodies may vary from valley to valley. The Serbian Tone system is recognizably derivative from the Byzantine system, but has elements of the Serb folk music tradition interwoven. The oldest Russian system of tones is preserved only in Alaska. The oldest in common usage in Russia, Znamenny, is much simplified from the Byzantine model.
We Antiochians in North America tend to use the Byzantine system, though some parishes coddle the musical sensibilities of converts and use Slavic tones, which sound more 'Western', and we have choir directors here and there that subvert attempts to introduce congregational singing (the old service books said 'people', not 'choir') by using ornate composed Russian settings the Sunday after the priest reminds the people they are suppose to participate by singing.
Basil Kazan has 'translated' old Byzantine musical manuscripts into Western notation (approximately--there are quarter tones in Byzantine music that can't quite be rendered): Tone 2 sounded that way in a lot of the churches in the Empire before ever the false prophet Mohammed darkened the earth with his ideas.
Fascinating. Thank you very much. Much obliged.