I have lots of experience with this sort of thing. I'd suggest no vocals to compete with the conversations unless someone specifically asks.
Ry Cooder & Manuel Galbán-Mambo Sinuendo(I think 2 tracks have vocals).
John Fahey-America
Michael Hedges-Aerial Boundaries
Miles Davis-In A Silent Way
Japancakes-If I Could See Dallas
Global Communication-76:14
Soundtrack-The Straight Story
There are tons more but these are mostly non-intrusive but engaging if you want them to be.
Ry Cooder & Manuel Galbán-Mambo Sinuendo(I think 2 tracks have vocals).
John Fahey-America
Michael Hedges-Aerial Boundaries
Miles Davis-In A Silent Way
Japancakes-If I Could See Dallas
Global Communication-76:14
Soundtrack-The Straight Story
There are tons more but these are mostly non-intrusive but engaging if you want them to be.