In MegaTraveller there was a sidebar that mentions the races that pre-dated the Ancients. Called the first starfarers, they were races that managed to travel interstellar distances using means other than the jump drive - STL ships, extremely long lives, electronic personality transfer are all emtioned as methods used by these races to achieve their intersteller status.
We know from OTU canon that fast STL travel is possible - the boardgames Imperium and Dark Nebula mention ships being able to achieve 0.9c, ehile other sources have more reasonable limits of 0.25 to 0.3c for STL ships - eg the ones that colonised the Islands subsectors.
So how about this.
A TL9 culture of cut off humans fails to develop the jump drive but does have the maneuver drive, gravitics and fusion power. As they exploit their home system they build lots of communication lasers. As they rise through the TLs and send STL ships to nearby systems - taking years to get there - they build laser relay stations between their STL colonised systems. It may take six years for a ship to make the journey to an adjacent system, but communication can now travel at light speed,
Along comes personality copying tech (wafer tech in T5/MgT), cloning and synthetic bodies. You now have the tech to send the electronic personality over intersteller distances, it just takes a few years.
Now think of it from the Envoy's point of view - their personality is copied, the original remains on their home world (stick them in cold sleed for the mission duration if you wat but it is not necessary). The 'clone' awakens the instant the download is complete and from the clone's point of view it was instant (time has passed in the real world). The clone has its adventures, the memories of which are downloaded and beamed back to the original if you want to, or the clone personality is copied and sent to the next world for the next adventure...