A group of people playing instruments.
Some people hang out together
People playing instruments doesn't lead me to believe they are specifically there to hang out together, they could be there for a very specific reason like a concert or a practice.
exists e1 x1 x2 x3 x4.(a_topic(x1) & of(x1,x2) & Theme(e1,x4) & Actor(e1,x3) & v_play(e1) & n_instrument(x4) & (x2 = x3) & n_people(x2) & n_group(x1))
exists e1 p1 s1 x1.(a_out(s1) & Manner(e1,s1) & exists s2.(Theme(s2,x1) & a_together(s2)) & Topic(e1,p1) & Actor(e1,x1) & v_hang(e1) & n_people(x1))