The 831 would probably be useful if you are working on a design with a seperate analog and digital section isolated from each other where the analog needs a split rail for the op-amps for example.
The 832 can do a split rail with its normally isolated 30V outputs connected in series (e.g. CH1+ connected to CH2-), but the 5V channel shares it's ground with CH2 so the digital side would no longer be isolated.
However the 832 has up to 60V at 3A available, and you can parallel the isolated outputs to get 6A at 30V. You can't parallel the +/-30V on the 831, so 2A max it is.
Also, I think the 832 is much more widely known and would probably be easier to sell on. It seems to have had quite a few firmware revisions and the heatsink fix. Also don't forget Rig
lol I don't know about the 831.
If it's the suppliers fault then I would return it for replacement at their cost. If it's your cockup then find out how much return post is and decide if it's really worth pursuing.