the OD9 is a 9 series remake of the Maxon OD880. i use an 880 on my board, and absolutely love it. it does sound slightly different than an 880...maxon says the spacing of the components affects the sound and the 880 is huge compared to the 9 series.
one of the coolest things about it is you can selelct the voltage you run it at. it's always 9v in, but you can flip a switch to enable a circuit that'll convert it up to 18v inside the pedal, like a real 880.
Not sure where you got this info, but the OD9 Pro Plus is NOT a remake of the OD880, according to Maxon
Maxon says it is a remake of the OD808, not the OD880:
The OSD-9 is the pedal that is a remake of the OD880- see Maxon link below:
meant to say 820, whoops.