For DolbyDigital, DTS, and ProLogic decoding, you want to use the Meridian, fed with a digital input. The 568.1 does not have any analog pass thru ability, not even for two channel. Therefore, I would never supply the 568.1 with an analog signal. The 568.1 is an accomplished DAC, so I wouldn't worry that the Sony could do a better job on its own. Besides, with the 568 you don't have an analog pre-amp anyway. The 568 digitizes ALL analog inputs.
The 568 is a nice piece of equipment.