I had to change the audio output on SD4700 to 6channel analog to hear the DVD-audio properly, that's because you are using the SD4700's dvd-audio decoder to play DVD-audio.
The SD3750 and SD4700 both use the same de-interlacer, Zoran Vladdis V.
FYI, Zoran is the same company that makes the decoder in Outlaw's DD/DTS Receiver(1050), which leads me to believe it's a very good, low cost chip. Zoran's de-interlacer may not be as good as the SAGE, but it's also not as expensive. With the Panasonic RP56 you are paying for a good de-interlacer chip and not much else. With the SD4700 you are getting more than just good video. It comes down to what's your priority.
The SD3750 and SD4700 both use the same de-interlacer, Zoran Vladdis V.
FYI, Zoran is the same company that makes the decoder in Outlaw's DD/DTS Receiver(1050), which leads me to believe it's a very good, low cost chip. Zoran's de-interlacer may not be as good as the SAGE, but it's also not as expensive. With the Panasonic RP56 you are paying for a good de-interlacer chip and not much else. With the SD4700 you are getting more than just good video. It comes down to what's your priority.