By "Poly", I assume you mean polyurethane. Remember, there are many, many "Poly's", to include -butylene, -vinyl, -isocynene, -ethylene, -propylene, etc. In fact, the prefix 'Poly' means 'many' or 'several' (smile)
sorry about the digression......
Unfortunately (or fortunately for many), once a coat of polyurethane is applied, it is VERY difficult to remove. There are no solvents that I know of that will remove it, as unlike laquer or shellac, it does not dry and cure by evaporation, but by chemical change. The only way I can think to strip the wood is through course sanding and gradually to fine sanding, with constant replacement of your sanding belts which will load up with the sanded off finish.
The best way to refinish, in my experience, is to sand it down with 240 grit and then with 320 grit or 0000 steel wool, wipe clean and apply another coat (perhaps low sheen this time) polyurethane in two light coats. If you're intent on getting to bear wood first, be prepared for a lot of work or perhaps it may be easier to just replace the wood work.