I always prefer to strip and then use the West, and have had great results.

 

I hope you used 320-400 or higher between coats, I also hope it was gloss not semi gloss. 5-6 coats usually fills the grain (you didn't say which wood)

Resin, meaning west epoxy? no can do. it has to have bare wood to bond. Also you would still need UV protection of the West system

Usually after 5=6 coats of finish I'll go for wet sanding or even automotive compound and wax on the last. It takes time to get that gloss.
you may never get that glossy glow with water based I've seen it get milky after many coats.

Note; many of us don't wait long enough for finish to cure.

 

Probably better not to chance it. The epoxy may tend to lift the urethane and at best, as Denise said, will likely not adhere well. I have used ZSpar Captain's Varnish OVER West System for the UV factor and it has held up very well but the other way around may not work. Maybe coat a small area first to see what happens.

 

epoxy over varathane is working backwards.varathane is a topcoat, not a substrate.

 

Epoxy will not stick to varnish. It is not intended to be used that way. Varnish over epoxy is not a problem.