The 12" woofer is necessary, it contains the FIR DSP and the power supply.
That is what I figured. I ran the whole J8 system together using the bottom to power the top.
I think you would be surprised what the 12" woofer is contributing. 2" drivers in the tops can only go so far and 100hz is out of the question.
I didn't use external subs the first time I ran the band on the J8's. It sounded good, but lacked punch. The clip light was coming on from the kick. This prompted me to run some external subs the next time.
I read that the internal crossover point KW181 is 100 Hz which is why I split the signal there. The internal crossover point for the J8 is published at 220 Hz. For the setup I was using, the bottom was covering the octave from 100-200 Hz... which has a lot of musical information (basically, an open A string on a guitar on up to A string12th fret). So, yes, the bottoms were still contributing in the low-mid frequency range.
If you had a better RCF subwoofer you would be really stunned. I have a bunch of 181 subs. They are 1 note wonders that don't keep up with modern subs.
No doubt a new set of RCF subs would take the system to the next level. The KW181's is what I have for now. I've been happy with them for the most part, however (not to highjack my own thread, see below...)
Of the four KW181's I have, three of them have had speaker failures. All three have failed the same way... adhesive broke free. Two of them had the magnets come free, the third had the plastic ring under the cone come free. I replaced each one with a Celestion FTR18-4080FD. I haven't had any problems with those. I don't run very loud, so I know I wasn't over powering them. I suspect the the failures occurred in transport. Pushing those subs over rocky parking lots results in a lot of vibration.