I apologize for bumping this old topic, but I have done quite a bit of research on this, so I want to share my experience.
I had recently brought all the potential candidates, unfortunately, the ailing CD3400 turns out to be the best sounding, followed by the Panasonic (couple different models have same innards, my sample was 870 - splash proof version of 570).The hypes from Head-fi prompted the inclusion of DT25. I won it on Ebay https://wheelstips.com/best-car-dvd-player and the seller graciously took it back, a lost of $10 shipping. The Sony skips at the slightest move, and the high frequency is rough, very antiquated brick-wall filter. One thing that I haven't tried: those portable DVD player may have better sound than CD player if used on CD only. Try the Panasonic/Sony/Pioneer without the screen. I was shocked how good a Pioneer $199 DVD player the 525 compared to my Philips SACD-1000.