Cambridge Audio CD4

I bought one of these very cheap off ebay as a stop gap when my second system Meridian gave up the ghost while deciding what to get to replace it.

I read that a "BNC cap plug" improves the sound....

Is this just a BNC plug to phono socket converter (hard to believe how it can affect the sound) or a BNC plug loaded with a 51 ohm resistor (which would make more sense as to affecting the sound quality)?

Any ideas or experiences please?