The RS (Release Sample) on the edit page adjusts the sound that the damper makes when it contacts a vibrating string after a key is released. The speed in which a key is released has an impact on the noise as well. -inf turns it completely off, which sounds very sterile and not like an acoustic piano. The release samples on the Fazioli F308 sound perfect (to me) at the default setting.
The Key Release Noise in the play page controls that amount of mechanical noise that is made by the action parts key/whippen/jack/hammer shank, etc., when the key is released. It's more of a thud sound. It's a noise that has nothing to do with the strings like the aforementioned release sample does.
God Bless,
David