Cubase 5,5,3 on mac Intel

My old Mac Pro G5 is out of order.
I have official Cubase 5 with upgrades on. (5,5,3)
I want to buy a mac pro 1,1 (second hand) it’s 8 core 2,66 ghz but 64 bit.

On steinberg they say cubase 5,5 N/A for 64 bits … does it means it can’t run on this mac because of 64 bits ?
in this case i have to buy a Cubase 6, but not running on 10,7 I suppose…
minimum 10,8 but for that i need another mac…more expansive grrrr… :imp:

What is your advice