You can use steel wool as a last step prior to waxing but you have to be very careful. The brand/type of steel wool you use as well as 'how' you use it makes a difference. Regardless of the brand, I would use nothing less than 0000 as a last step. It must be oil free!!!! I've had very good luck with this product from Rockler: Liberon Steel Wool-#0000 Steel Wool | Rockler Woodworking and Hardware
There are other long fiber steel wools out there, but I've no first hand experience with em.
First and foremost, leave your project dry thoroughly. Give that poly a chance to completely set.
Off the shelf steel wool's as mentioned have a tendency to break down in use. You'll run the chance of embedding small steel fibers into the project. Very light pressure is the key when using any steel wool. Too much pressure or spending too much time rubbing in one spot will rut on you in quick order and with poly's ghosting comes into play. Ghosting is what happens when you rub thru a top coat of poly into the 'layer' below often leaving a faint white ring around the area sanded thru. All wipe on products and aersol's for that matter are thinned out considerably in order to facilitate the application. So often several more applications are required to achieve the desired finish or a workable thickness. I'm happy with using steel wool to just knock down the nubs and fuzzies prior to moving on with the finish schedule. I don't use steel wool's on semi-gloss, gloss or mirror finishes.
CherryvilleChuck mentioned wet sanding. This is my preferred method in conjunction with a automotive polish finish schedule when a top shelf finish is desired. Alot of work, alot of time and elbow grease required, but dang, the results speak for themselves. You could certainly use wet sanding to flatten out your surface prior to waxing and have a very nice finish! Works very well on satin finishes with up to 320-600 grit papers. Semi-gloss up to 1000 grit. The higher grits on serve to bring out the intended luster of the finish. Higher grits do not add to the sheen.
Stick mentioned pumice. I've experimented a bit with pumice/rotten stone and a felt pad. Having some really nice results. I just havn't gotten a good schedule (sequence of applications) down yet.
Just bout all finish schedules require two things. First, knowing what you want and second, knowing how to get there.
Good luck with whichever method/means you go with!!!!