I am asuming you are sourcing from Central Valley of California (CA) and are buy in 36Lb Lug/Cases IF so you will need 3 case for 23L/6 US Gal of finished wine: OR
6-7 cases for 54l /15 US gals Notes: Cab Sav give the greatest body + berries , but needs more time to mature. The Caifornia- Central Valley Cabs generally don't have much varietal flavour(Over cropped/irrigated) Most like to be from middle aged vines
7+ years old
The Zin will give (some times) Spicyiness and Berry flavour. Also if from Cnetral Valley CA.are most like to be from older vines(15Yrs +) than Cab or Syrah , so have more favour/ concentration. Depends on specs.
-Most Homewine Makers I know have made wine with these grapes with good sucess.
The Syrah will give spiciness and more subdued fruit flavour. Will also likely be from the youngest (3-7 years old =least concentrated) vines if from Central Valey CA.
May be 1/3 of all the above.