I had the SX510 once.
My feelings.. well, I and this one didn't get along well at all. I much prefer the CT570 or the CT780's sound over this one. The SX510 isn't "sweet" in the typical Panasonic manner... it's weird instead.
The SX510 only has non-linear anti-shock (either that, or no anti-shock), and the quality of that is inferior to the same function on newer Panasonics. Some kind of distortion (hiss?) is easily heard depending on your CDs.
So, based on my memory, I wouldn't recommend the SX510. The Japanese version does have optical out; not sure about the non-Japanese ones.