No, I didn't test the comb filters because of limited time and because the X9 owner had a lot of experience and said the composite out was much better for image quality.
I'm also an X9 owner, and while the results using the composite output might look better at first glance in some circumstances, I don't recommend using it.
The X9, like most other players with both composite & S-Video output, does not have direct composite (also called pure composite) output. This means that instead of the signal path being disc->TBC->output, it's disc->TBC->3DYC->recombined signal-> output. So the composite signal is just the S-Video signal recombined back into composite.
I've comfirmed this on my own setup (you can tell what recombined composite looks like after you see it enough times on different LD players), and I believe it has been confirmed on the repair manual of the X9 as well. You can talk to someone like Kurtis Bahr for more information, he's repaired and worked on a lot of players including the X9. I believe his contact info can be found in a past post on alt.video.laserdisc.
If you absolutely need to use composite, you should use a players with direct composite like the Pioneer Elite CLD-99 (CLD-HF9G in Japan) or the X0 (BNC terminal output only).
Sorry I didn't notice this thread earlier, I don't visit this forum much.