I always kind of figured that in the case of the Bard, while they use physical implements like arrows and probably traditional forms of poisoning them, that some of their fancier attacks were aether imbued, as well as weaving a degree of aether into their songs. Though since they are not outright spells, I imagine they use their own aether, and it is at a lower cost than it would be for casting classes. Empowerment more than outright casting.
Likely this is part of what sets bards apart from mere archers besides the usage of songs.