If you want to understand why some finishes work, and why they work,
then I recommend this book above all others: "Understanding Wood
Finishing" by Bob Flexner.

I have a lot of books on this subject and have been refinishing pianos
most of my life.  I still learn something new or I forgot every time I
refinish.

There is no magic bullet and I avoid all poly finishes.  Poly looks
plastic like and that's just wrong for antiques.

Don Teach
Shreveport, Louisiana