Most impactful for playing soft

Hi, my system is primaluna evo 300 separates with b&w 702 signature speakers.  I normally play music from a blue sound streamer through a ps audio nuwave dac.  When I play my system loud it sounds great to me, but when I play it at volumes my wife can deal with it sounds a bit thin.  What single upgrade would people recommend in order to most directly address this low volume problem.  I listen to heavy metal, r&b, rap and jazz for the most part.