Any significant change in distortion when you run the Stingray in Ultralinear? At 86 db, your speakers might be over-taxing its 18 watts in triode if you're playing loud in a large room. Probably not the problem--the sound would likely be kind of flaccid at the frequency extremes rather than shrill in the highs--but it's worth checking.
As dover said above, what gain setting are you using on your PH1? If you're on high, you're probably over-driving your amp's input, since your cartridge is high-output at 5 mV. That could make the sound shrill.
Your loading isn't a problem because 47K is what your PH1 gives you and also what your cartridge wants to see. Your 4-inch thick maple slab isn't the problem--if anything, the additional mass would emphasize the lows, not the highs.
Otherwise, it sounds like a stylus/cartridge issue. Make sure VTF and is in the middle of recommended range (to start); and set anti-skate to zero or barely above zero just to see what's what, and then gradually increase in tiny increments to see if it helps. You probably know these things already but they're worth a reminder.
Good luck!
As dover said above, what gain setting are you using on your PH1? If you're on high, you're probably over-driving your amp's input, since your cartridge is high-output at 5 mV. That could make the sound shrill.
Your loading isn't a problem because 47K is what your PH1 gives you and also what your cartridge wants to see. Your 4-inch thick maple slab isn't the problem--if anything, the additional mass would emphasize the lows, not the highs.
Otherwise, it sounds like a stylus/cartridge issue. Make sure VTF and is in the middle of recommended range (to start); and set anti-skate to zero or barely above zero just to see what's what, and then gradually increase in tiny increments to see if it helps. You probably know these things already but they're worth a reminder.
Good luck!