Rich,
Being a user of microphones in general, I will jump in here.
The phantom power that the microphone needs, is used to power the electronics in the mic, the actual output from the microphone is low and needs a pre-amp to bring it to line level to plug into the Soundblaster card (line input). The RS SPL meter has it's output at line level so should work directly with the soundcard.
The phantom power is only passed on to the microphone via the pre-amp and does not get fed into the soundcard.
Soundcards expect high impedance microphones, but the Behringer ECM8000 is a condenser microphone with a low impedance, so even if you could provide it with phantom power, it would not drive the soundcard microphone input.
You should be able to get a cheap pre-amp that supplies phantom power to suit your needs and could even be battery powered.
For an example of a pre-amp with phantom power:
http://www.boomerangsounds.co.uk/pro...d=275&xSec=140
Hope that helps, I am new to the Shack myself.
Mike