ohmage vs. wattage?

They will receive roughly 400 watts a piece, probably a little less, but there won't be an audible difference.

I assume the 800 watt rating is peak? Use the rms numbers on both subs and amps.

No calculator for this that I know of.  It's just simple math, though, but write the results as you go through it.  You know what the rated output is at 2 ohms.  Now look at the rated output at 4 ohms.  Subtract the 4 ohm from the 2 ohm.  Divide that answer into two, and then add that result to the 4 ohm rating.  You now have an extrapolated 3 ohm output.

Compare the 3 ohm to the 2 ohm outputs.  Divide the difference between them by three to get  thirds.  Add one third to the 3 ohm output to get a 2.67 ohm result.

You can't extrapolate another "rated" output from only one given rating...but you can come up with a good guess as long as you have two ratings to work with.

heh heh....or do like wrathchild did and come up with the answer in your head.