Musicians doing with they do best.
Musical instruments are in the room.
If musicians are doing what they do best, it is implied they are using musical instruments.
exists e2 e1 s1 x1 x2.(n_thing(x1) & ne_nam_musicians(x1) & a_best(s1) & Manner(e2,s1) & Actor(e2,x1) & v_do(e2) & with(e1,x1) & Actor(e1,x2) & v_do(e1) & (x1 = x2))
exists p1 s1 x1 x2.(n_room(x2) & in(x1,x2) & n_instrument(x1) & a_musical(s1) & Theme(s1,x1))