Why would my D406 produce a better picture than my D703 and my DVL 700?
I'm not sure how to describe the picture differences. Same laserdisc is being used in each machine, same display/picture mode used on my LG. Composite input used. The 406 is relatively sharp and clear. The 703 and the 700 pictures are noisier (?) is how I would describe it.

But is everything else the same????
Same cables, same connectors i.e. Yellow video on both???

Also it could be that since the 703 will have better internals in the way of video processing etc. you may need to make sure your
TV is calibrated properly to that player first then try the comparisons.

I'll never forget the time I had to get my R7G serviced and was playing a 503, the 503 gave me a better image with same cables etc.
Going into the projector, but then I realized that I had not adjusted the projector to the new room and after that was done the R7G
blew away the 503 even with composite Yellow video.

Try a cav disc on both of them. 703 might be out of alignment and cross reading on clv discs which causes noise like artifacts

same cables, same disc...same inputs. I'm just swapping them from machine to machine.
I pulled the cover off my DVL 700 and played with the tilt adjustment and the focus adjustment on the board, making a note of their original positions. I could make the picture horrible but could not improve on the picture beyond the way I originally described it. Noisy. I've not looked at the D702 internals yet for those adjustment options

Don't tweek stuff, you are better off selling it than tweeking.

As substance said do the CAV disc and tell us what happens.
Then make sure your TV is calibrated properly.

No sense in trashing a player because you don't have time to adjust your TV but have time to tweek the pots

I could understand the 406 having a better picture than the DVL-700 or at least just as good as the DVL-700 was based off the CLD-D604. Now for the CLD-D703 the first thing you need to do is turn OFF all the DNR processing in the 703. If the DNR is being done in the 703 and then the TV digitizes or even performs DNR itself the picture will be worse, you always want all DNR done at one location.

With that said if the 703 or 700 laser are not aligned as good as the 406 the 406 will have a less noisy picture.