Regarding Volero: they could play in Hallenstadion, despite it might be a bit oversized (icehockey is main user, around 15.000 seats (!)).
They were already once F4 hosts a number of years ago, and so far I know it is the fourth consecutive time they play Istanbul in Playoff 6, despite it was not always, but mostly VakifBank. Hey, if they want to win, they have to beat also VakifBank, so difficult this uphill battle will be...
Sorry, despite it is indeed Voleros 4th consecutive Playoff-6 appearance (and without that former F4 hosting they never reached that F4 again), but in 2014 they lost not against Istanbul, but against later winner Dynamo Kazan in the Playoff-6. After that it was one time VakifBank already and one time Eczacibasi.