Charles, welcome. There're several possibilities at this time as to why you're not totally overwhelmed by your M80s, but inadequate amplification should probably be placed at the bottom of the list. Your DA3ES is now somewhat dated in its features, but furnishes heavyweight basic amplification typical of the Sony ES models. Your M80s are slightly above average in sensitivity and unless your listening room is huge(unlikely if you previously used bookshelf speakers)the DA3ES should have more than enough maximum power capacity to drive them with ease.
Pending your purchase of a replacement receiver with updated features you should experiment with speaker placement as Shawn suggested, which can indeed make a significant difference. Also, even with speakers as excellent as your M80s there's a need to guard against unrealistic expectations if you're not immediately "blown away".
