If you're in the U.S. or Canada, none of those Panasonics have a line-out at all. Thus, you'll have to rely on the headphone-out as its only audio output.
For example, I own both the current top-of-the-line Panasonic (SL-CT790) AND the current top-of-the-line Sony (D-EJ1000). The Sony has a line-out; the Panasonic doesn't. Surprisingly, the Panasonic has better sound from its headphone jack than the Sony - in fact, it is similar to the sound from the older SL-CT470's headphone jack, but at a lower maximum loudness level. (The Sony EJ1000's headphone-out sounds dark and grainy by comparison, with emphasized mid-bass and rolled-off highs.)
When the Panasonic CT790's headphone-out is used as a line-out, and used with my Headroom Total Airhead amp, it sounds remakably similar to the line-out of the Sony EJ1000 except for a lower loudness level and slightly grainy highs.
jlo mein had compared his sister's SL-CT590 against his D-EJ1000 - and out of the headphone out he slightly preferred the CT590 to the EJ1000 (warmer and smoother on the CT590 versus grainy on the EJ1000). But he much preferred the EJ1000 to the CT590 with an amp; the CT590's sound became boomy when an amp is connected to its headphone-out.
