[Anthony]

Speaker Workshop.

REW can do the frequency response stuff, but SW can measure driver impedance, driver FR with established start/stop frequencies, and with a jig, you can use your soundcard to measure resistors, capacitors, and inductor values.

That, and it has a great crossover design tool and can measure driver distortion (both harmonic and intermodulation).

Basically, I got as far as I could with REW (from a speaker design perspective), so I decided to try SW. REW is still #1 for room measurement and subwoofer EQ, though.