PL560 is a true classic performer and doesn't need upgrades. It can be part of entry-level or more advanced audiophile system. The condition of deck needs to be examined and probably lubricated/serviced. They can have speed control issues and that can be resolved as well. In fact I was bringing PL560 to the original performance with all functions work mint. This deck is 100% serviceable and has superior built quality (check ebay prices to appreciate this unit and quit thinking about another one!)
M97xe is good cartridge as long as it bears original made in Japan stylus in good shape. You may also remove stylus and shoot some DeOxit spray inside, than let it dry and mount stylus back. Headshell can be unmounted from the arm to inspect stylus condition. I use pocket jeweler's magnifier to see wear. Bad stylus may be the reason why you're not satisfied. Check the original stylus availability -- you may check needledoctor.com for good one.
AVR phonostages may/maynot be OK, but would suggest $100...$200 outboard units such as ProJekt phono box or Bellari
This turntable has may various cartridge options to choose from, but first make sure your stylus is lookin' sexy :-)