How much improvement with better toslink cable?

You might want to try an Amphenol glass cable just to put your mind at rest. There is a source for these if you to a search for Amphenol in discussions.

I believe I did detect a difference going to glass, but you must make that call yourself with your system.

I can tell a definite difference when using a Virtual Dynamics Master digital cable in my system on some recordings.

I cannot tell any difference in clarity, but I like the way the VD cable presents its sound stage differently. To me it seems that each instrument is not only in its own space, but that I can focus in on each musicians feelings of the music. I don't get this on all cd's, but I do notice this when using the Virtual Dynamics cable. This probably sounds absurd to some of you, but I can tell the difference and I know it is not just about the ones and zeros.