Outboard D/As - Why? (Convince me...)

What commercially available outboard D/As can anyone suggest which will absolutely convince me that the quality of the internal Sony D/As on the 220-270 series units are easily surpassed?

Which elements of the listening experience am I missing with my plain old 'pedestrian' 270?

I'd like to visit a showroom for a demo, but need brand & model info in hand in order to fend off the sharks that invariably inhabit such places...