When you are using SCART, you'll get RBG output. There's (probably) no CVBS in the NMS's SCART at all, that's why your adapter does not work. Even if there was CVBS in there, well then the adapter would work, but the point would be moot since the quality will be exactly the same as from the DIN in th 8235 or RCA(C-INCH) in the 825X. The connector itself does not make the quality any better
The NMS's probably don't have S-Video also at all, since the RGB is superior in quality to S-Video, and RGB was very common in TV's the days they were built (much more common than S-Video support), so adding S-Video to the connector would have served no point. So an S-Video adapter won't work either.