The whole digital board is different. I don't notice a significant difference between my AP1/PP and the USB 32 in all honesty. The AP1/PP is slightly better, but definitely not $1k+ better, which is not its fault, but more so a reflection of the improvements in the M7's design. I'm excited at the possibility of an OR5 bringing the M7 up another level, as that is exactly what I'm after.
Many thanks for your AP1/2+M7 impressions. I agree that the USB32 implementation is very good. The A-gd DI-VI3 has improved my old A-gd DacOne to a whole new level.
I have been considering the OR5 I2S path for my M7 as well but still not sure about the investment. I am glad that I can exclude the AP1/2 from my list because the AP1/2 investment seems unjustifiable for the M7. I will wait for more impressions with the OR5-I2S-M7 combo :)