I use REW (Room EQ Wiizard) nowadays for measuring, never tried it on Mac but the OS is supported. If you haven't used the V15-700n yet, the low frequency response tends to approve in the first ~10 hours of use.
@Bee: Good to see you're still around! How's life?
Measuring T/S-parameters is always wise, can also be done in REW if you can get it to work for you. The V15-700n is used in a reflex and band pass bass cabinet, so that will typically mean it's either (most) suitable for Extended or Extra Extended.
I am sorry for answering so late, i had holidays. Reason for the Cubo 15 ext. with bigger cutout was just that this one was already built and usable as a test cab.
I have not compared Cubo 18 to BR with the same driver, because both were measured by a friend who lives some 100 kms away from me. But i really do like my Cubo 15s with Kappa LFA. Because of the lower need of xmax, they tend to sound a little more effortless compared to BR. The other notable thing is the higher part of 2nd harmond distortion compared to 3rd, while measured BR gave more 3rd than 2nd. In my experience that leads to a "warmer" sound. Only downside is, that my Cubo 15 with Kappa LFA and the Cubo 15 ext. with Colossus both had -3db points at 47 hz which isn't too low. But it's right that they tend to "sound lower". The -3db Point on LF18N401 was about 43,5 hz btw.