I've been playing with this myself. The minwax wood hardener seems to work but doesn't fill in the pores of the wood like you have seen on the stuff the pro's do. I have treated some punky spalted maple and the wood, while much harder, is still soft enough to dent with a finger nail. Color and grain is enhanced a bit. I believe this will work fine with woods that are fairly dense. I don't see it as the best solution for soft or punky wood. Wood Hardener is toxic and eats plastic right up. I cut a scale from a treated block and coughed for a half hour afterwards. I think this is nasty stuff you don't want to spill on you or breathe for any length of time.

There is also something called Pentacryl and Polycryl. The Pentacryl will stabilize wood but does not harden wood. It acts by replacing moisture in the wood. It is non-toxic and easy to use. If you leave wood in the solution long enough, it will wash out the color of the wood. If you leave it in long enough to treat (few hours or day or two depending on thickness), it will slightly darken the wood, and I think, enhance the grain nicely.
Polycryl is a companion product to Pentacryl that I haven't had a chance to try yet. It is designed for soft wood and will harden via polymers left in the pores of the wood. It looks encouraging.

Last, but not least, Loctite makes a porosity sealer called Resinol 90C. Manufactors use this to treat a porous item, usually metal, to seal leaks. You apply it, heat it to 90 degrees centigrade and the Resinol turns hard. Several makers speculate this is what at least some of the pro shops use. It is only available direct from Loctite, 4 gallon minimum and it is $70/gallon. I am interested in trying this stuff, but not 4 gallons worth. Hopefully some makers will go in on an order to split and try it out. If some one is interested in getting some, let me know and I'll dig up a name and phone number for you at Loctite.