It's pretty common to have to work in a room that is multi-use. In other words, a room that is not outstanding for anything!
Here I always use ORTF as a main pair and I make sure that it is hanging over the lid of the piano. Then 2 omni outriggers to be able to goose up the sound of vln and vlncello and provide width.
Mono omni spot on the piano (in crook) gives detail and real bass while ORTF pair above piano supplies the Left-to-Right feel.