At the scale of interstellar trade or exploration, there are a few reasonable situations.
If there is FTL, physics is extremely strange and not at all like what we expect. A reality check in this case is difficult.
So, assuming no FTL, interstellar trips will involve tiny self-replicating hardware "seeds" that grow into a civilization. Machine intelligence, in short.
Now, it may turn out that organic or hybrid intelligence is more efficient than machine intelligence at a myriad of tasks, or that uploading "real" brains to an emulation layer is the most efficient way to get intelligent actors in the machine.
I will assume that growing intelligence in a machine may be wasteful, because real intelligence requires something as complex and rich as reality to grow, while maintaining and training existing intelligence is much easier.
In this case, the aliens could enslave humans for brains. Humans consume a biosphere, which doesn't use much in the way of resources that a star-wisp civilization needs to replicate, but still generates intelligent actors.
So the star-wisp civilization doubles itself a few dozen times in space, builds an invasion force, and invades the planet. There are only a few true intelligences, but a myriad of "smart bots".
They descend upon Earth and harvest our brains. Maybe they start with voluntary uploads, but given how weak our defences are decide that it is more expedient to just upload almost everyone and discard the unsuitable. A breeding population is left behind to provide for further harvests.
The generated intelligences are modified and trained to do tasks and have loyalty furthering the production of starwisps, solving certain categories of problem that require true intelligence.
The orbital civilization bootstraps up to somewhere between K1 and K2 level, then starts launching further starwisps. It is a race, because there are other starwisp lineages that are also spreading out, and the faster you get 1 or 2 out there the more likely you get "ahead of the curve"; and if behind the curve your starwisps arrive in an already colonized solar system and your lineage dies out.
Once this first wave is complete and a few dozen starwisps are sent out, the solar system fortifies against other starwisps arriving and starts a colony of the original aliens. As noted, the most efficient way to produce new intelligences is to grow them organically, so biospheres are built, artificial bodies are created, machine intelligences downloaded, and children are raised.
Enslaved human minds remain useful during this period, but are reduced in importance as more and more of the intelligence requirements of the hybrid civlization are provided by their own biological creatures. Terraforming of planets is started (as they are more robust than orbital habitats). Once a few stable biospheres on planets or moons are robust and up and running, the terraforming of Earth begins.
This results in the extension of the human lineage, but by this point they are no longer of economic use to the aliens.