varathane/urethane question

[Thor]

I'm almost completed my new basement stairs ,(still need to install riser boards) made from white pine. I've applied 5 coats of a professional varathane but am disappointed with the durability of the finish.
I am wondering if it is possible to apply a 50% pure poly urethane over top of the varathane .......such as Gym Finish. Will varathane and urethane bond together ? Will the urethane give the harder finish that I'm looking for ?

I posted a photo in the forums album titled stairs in "questions category" , for some reason it wouldn't let me upload the 2nd photo. So here is a link to another view of the stairs
http://users.vianet.ca/thorr/new%20basement%20stairs%203.jpg

[Rich]

Polyurethane, varathane, and urethane are all derivatives of varnish. They all have varying degrees of durability, yellowing, and some others. But as far applying poly over varathane - there should be no problem. Try and put a light sanding on your last coat before applying the new coat. If not it will tend to grab the last coat and makes it almost tacky - most likely you will end up having brush streaks.
Urethanes are really good for floors and where you will need durable surfaces.