Hmm, that theory on Etruscans sounds dangerously close to the Illyrian theory of origin which claimed Croats were descended from the Illyrian people of the Adriatic, perhaps backed up by the Dalmatian romance language? (or was this dying language a Roman/Medieval product)
Regardless, it has as much validity as the polish aristocracy believing they were decended from Samaritans...a way to be non-slavic, or have greater traceable roots.
Well, I have here Bohyslav Chropovsky's The Slavs: their significance, political and cultural history, and although I fear the findings of a book published in 1989 in Czechoslovakia might be too baised for some sort of Moravia origin..

That said, it mentions a number of theories for the original Slavic homeland (and perhaps the people that would become the Slavs...or at least, a point on their migration that we have evidence of...)
The Vistula-Dnieper theory where the Slavs were on the river basin of the Dnieper some time between 1500BC to 500AD. (blame the length of time on scholarly arguement)
The Oder-Dnieper theory is another one, though most people agree to an early middle age time settlement.
The Dnieper theory holds Slavs existed on the Dnieper basin from earlier then 5th century BC.
The Oder-Vistula theory has their home originally between the Oder and Bug, around sixth to fifth century BC. (claims Germans pushed them out)
Chropovsky here seems most excited, however, with then Danubian theory.
He then proceeds to explain that the Balto-Slavs, or Ancient Slavs probably existed on the above territories by the end of the second millennium BC, until language divisions grew to split the Baltics off from the Slavic language, which was developed in the South.