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?
I believe they where, DS9 was on its 6th season and Voyager was on its 4th season when the decision to switch to producing practically all FX shots with CGI . There are still some practical effects in the first half of DS9 season 6 i.e. the ketracel white asteroid.