The most westward penetration of any Slav group was a few miles west of Paris but they soon disapeared from history. The most southard penetration was Crete. Anything in between is a posibility.
Also an important aspect of Slav settlement is that it has often been described as a slow trickle rather than a full blow invasion. The Croats, Serbs are Bulgarians are (I think) only ones that migrated forcefull to their new homelands the others just seams as if they have sprouted out of the ground.
Sure there were raids into ERE in the second half of the 6th and first quarter of the 7th century but these don't compare to Vandal, Ostrogothic or Vizigothic invasions.
In order to get the Slavs moving you need to get the Germanics moving south and/or west to allow them influence history. Otherwise they just spread into north-east and continuing to coexist with Balt and Turkic-Iraninan speaking groups on their northern and southern borders.
As far as different focus of movement it would depend greatly on the choices of Avar expansion. Should the Khaganate make a serious war with Langobards I can see Slavs eventually overrruning northern Italy.