They used CG throughout the show, but only started using it heavily for space VFX in season 6. They used plenty of stock footage in the last two seasons, so it's not like they went full CG at some point.
You telling me the huge space battles in The Way of the Warrior
and in Call to Arms
were done with all models instead of CGI?
As is my understanding of it, yes! Incredible, isn't it?