Your model 7506 headphone set was designed to be a studio type of phone with somewhat higher impedance and lower sensitivity than a lot of headphones because the equipment it would be typically used with has sufficient output capability and a slightly less sensitive set will reduce the potential for disagreeable electrical noise pickup. I don't think Canon publishes the output impedance specs for the 80D but I suspect like a typical smartphone it has an audio output stage fed with low voltage and not capable of developing a great deal of voltage across the 63 ohm 7506 and prefers a lower impedance reproducer.
If possible, I would take your DSLR to some place like Best Buy which probably stocks at least a few sets of phones and you could try a few to see what works best in terms of volume and reproduction accuracy. Also note that when you see the load impedance listed in the specs for a set of phones this is at only one point in the audio range, commonly at 1 khz., and the impedance does vary wildly across the audio range for both headphones and loud speakers. So going purely by spec when trying to order may not result in the best outcome so testing is far preferred.
Rodger
EOS 1DX M3, 1DX M2, 1DX, 5DS R, M6 Mark II, 1D M2, EOS 650 (film), many lenses, XF400 video
