9833 has 6 channel time correction versus 4 channel on the 9831, it has a 6 position active crossover with a variable 24 db slope, whereas the 9831 has a 3 position crossover with no slope adjustment
9833 has the ability to go into "pro" mode and act as a passive crossover for your entire system, allowing you to remove the crossovers on your components.
9833 has a 5 band parametric EQ, 9831 has "bass" and "treble"
The full specs are available at
www.alpine-usa.com
There are quite a few differences between the two!