Onkyo TX-SR606與NHT Model1.3喇叭用Pure Audio模式時的疑問

唔知點解用晒5隻喇叭時播歌時就好好地,但係一用Pure Audio模式時D聲就
會好沉好濛,有冇朋友知點解呢?Thanks a lot
順帶一問想換過隻中置+超低音+後置環繞聲,BUDGET大概$5000
有冇好既推介呢?