hifi engine

What's the difference between Sony's CDP-XB740 and CDP-XB720 ? (and why the filter?)

Hi,

I was looking for the CDP-XB740 Service Manual, but could only find the 720 manual... What's the difference? Does anyone know? Thanks!!

Kind regards,
BJ

PS: What's exactly the use of the filter switch on the front? Does anyone ever use it? Can you hear/tell the difference? When to use it? Thank again! :)