No one has replied and, although I've never used the stuff, I'm interested, too.  I think you're talking about CPES (Clear Penetrating Epoxy Sealer) and i think it's more commonly used under painted finishes.  At first guess it seems redundant putting one epoxy product over another but would like to know about other builders experience with it.

Yes, that is the product.  It is also used uder varnish.  I have used it on wooden boat repairs, and it is a great product.

West System has a paper on this topic on their website.  It seems that penetrating epoxy has a lot more solvent in it than high solids epoxies like West, MAS, etc. so really you are paying extra for something you could mix up yourself.  They also weren't able to show much added penetration after the solvents flashed off and the epoxy hardened.  You might want to give their tech people a call.

Their website had articles dealing with diluting their product to make it a penetrating epoxy.  I was really talking Smiths penetrating Expoxy.