Unless you bought the P5W DH motherboard ages ago, as in. over three months ago, it should well just run it out of the box. Mine did, bought in August.
My GX2 only displays one temp in the nvidia control panel because it reckons that it's one card. If you get something like everest, it'll show you both of them.
It sounds like it's literally that the SLi functionality isn't working for some reason and that's one of your cards running and giving you that score. As that's pretty much spot on what the score should be in single gpu mode.
Honestly, I couldn't say why if you've made sure that in the driver control panel, you've turned it to multiple gpu mode.
The only setting I know that'll override the option in the panel to turn it from multiple to single gpu mode, is enabling the highest "SLI" settings of both AF and AA in either the general profile or the 3dmark profile. When those are enabled, as far as I'm aware, it doesn't use the second card/gpu for actual rendering? I haven't read into it, someone who has would be able to explain far better or tell me if I'm lying.
I would recommend some heavy searching of this forum and some googling, because I know I've seen a whole bunch of thread titles with this issue.