In my experience, if issues persist even when using an Extron interface, the problem is more serious than a dirty sync signal.
With my Extron interface I can feed it a horrible signal from one of my diy poorly grounded rgb cables without any shielding and still get the clearest image possible.
I use it with my PS2, PC with Groovymame and my Neo Geo MVS / supergun. My two main monitors are a tri-sync crt arcade monitor (that can take a 1v or 5v rgb signal) and an Ikegami TM20-90r broadcast monitor. I get a perfect image on both with all three machines.
Issues like distortion at the edge is more of a crt related issue and can not be solved by cleaning up the signal. I am no expert on interference but with my stuff, that kind of thing is usually solved with proposer emi shielding and making sure all magnetic sources are moved away from the screen.
My Ikegami monitor is fully shielded but my arcade monitors do not like being near my LCD screens or speakers etc.
It wouldn't hurt to try using the monitor in another room, testing sources with other monitors and testing other sources so you can narrow down where the actual issue is. Once you start getting into dry solder joints and looking for shorts, I have to refer to others.
With machines like a PS2, you can get high or low voltage issues by using the wrong RGB cable. If I remember correctly, a PS1 RGB cable had different resistors to a PS2 rgb cable. Arcade PCBs put out a 5v rgb signal so, to use one on a consumer tv or monitor, some type of step down is needed (like they have on superguns). Conversely, consumer consoles often look very dim on CGA arcade monitors made for a 5v signal. Ultimarc sells a signal booster for this purpose (pc on crt cga display).
I don't use professional monitor, but SONY CRT consumers, one projection 53" and a 38" tube, so it's a little hard to try change the room hahaBtw, if i remove EXTRON from chain, the image is really clean. I'm using shielded cables and a decoder based on BA7230 (RGB to component).
Sounds like your Extron is broken, or the dip switches are set wrong (inside or out).
I've used my Extron interface with Sony CRT TVs, pro monitors, arcade monitors. all without issue. It works with my Supergun, my PC and every game console too.
As they are so cheap, it's worth buying another to try once you have checked the internal and external dip switches.