Megaman X4 on Saturn has some extra background layers and effects in some stages. For instance, the second part of the first stage (with the fire in the background) features some nice warping effects on Saturn while it appears static on PSX.
PS1 versions are better IIRC. Them transparencies.
I don't remember if there was additional content on Saturn.
What are you using as a comparison? The PS3 can produce fully digital, uncompressed audio from its HDMI port while the Saturn is limited to analog stereo (which can still sound amazing, of course).
It sounds crisper somehow. Could be that I have a crappy HDMI cable.