1. reading the datasheets, it seems like the Stereo 2 way PEQ 2.1 can do everything the Stereo 2 way PEQ + have the OPTION of combining outputs 1 and 2 to a subwoofer signal?

2. additionally, isnt this the same as not mixing outputs 1 and 2 but connecting both outputs to a subwoofer, which will convert it to mono anyway?

thanks

1) Yes, that's correct, 2.1 just converts to mono. There is also a selector to toggle between stereo and mono.

2) No, for mixing 2 signals, you'll need a resistor network to be able to mix both signals. Connecting both of them to an input will not mix the signals.