I'm of the opinion that while the Ancients discovered subspace quite late in their intersteller expansion, when they discovered it they made more advances in subspace tech over a shorter period of time than the GTA/PVN did.
Also, I'm of the opinion that the Ancient Narrator was being poetic. Rather than taking the Ancient Lady's words at face ear value (since we never actually see her), I think she was being a bit poetic about their reach into space. I have no doubt that they spent thousands of years speading through their home system. Remember, their is more to a Star System than just it's planets:
Heliosphere: 80-200 AU
Oort Cloud: 2000-50,000 AU Possibly, even 100,000-200,000 AU
Sol's Roche Shpere (the magnetude of its gravitational influence) extends up to x1000 the distance of the Heliopause