Would Sennheiser PX-100 headphones work greatly as binaural microphones while wearing them

 

At your risk. Please take all safety precautions including isolating the headphones with a great quality signal transformer.

Would the 3D recording sound great?

All needed may be to convert the 32 ohms to 200 Ohms with a great signal transformer for each drive unit. They with the isolation provided too to send the signal to the preamplifiers which better have input transformers too.

In an older euroelectron post the same is suggested for HD-580. It sounded interesting on drums but if memory is correct there was emphasis at low frequencies compared to the great sound of higher frequencies.