If you do not wish to use the sound card for such measurements, you may use a sound level meter that has the capabilities to measure 1/3 octave bands to do the level and background noise measurements. If you compare this to the same measurements done with the hardware we recommend you should find that the sound card based measurements are as good. We have also done several comparison measurements with the most expensive analyzers for such kind of measurements and the results have been the same.
We have plans to approve a complete WinMLS-based system for building acoustics. Please contact us if you are interested in this.