The Sabres don't need a partner for Dahlin.
Andersson, however, is exactly what they need to get Owen Power back on track.
A signed Byram for a signed Andersson makes a ton of sense to me for both teams.
People are going to quibble because they have skewed views on one or both of the parts, or because their goal is to "win" the deal in some kind of imaginary internet GM game.
But each player has similar trade value, each is being shopped, and each is pretty much exactly what the other team needs at this particular point in time.