Capacitor

100uf 6

Are you sure its 100uf.
Thats a  lot of uf's. My Seas W18E001 woofers take either a 10uf or 8uf, I am running 12uf, Mundorf SESGO and Supreme Silver Oil
Best  caps for rock solid bass

I've found the copper foil in oil caps from companies such as dueland, Jupiter and miflex sound the best, but these can get quite expensive and are quite large

VERY Expensive. I prefer Mundord SESGO or Supreme Silver at just alittle less cash and stunning results. 

Mundorf Mcap,

I've tried Mundorf's lower priced caps, Not even close in perforance to their top of line SESGO and Supreme Silver Oil. Another member here swears by the SESGO, and he is correct, they out perform the Supreme SilverGold. 
Something about the EVO winding tech withina  Supreme casing, makes the superior sonics. 
Not cheap, but well worth it for the nuances. 

Alumen Z are not cheap

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These are the caps Troels Gravensen employs, 
No not cheap at all, , I went with Mundorf SESGO and Supreme Silver Oil.
Which out performed Mundorf's Aluminum caps 
The SESGO are about same price as Zcaps. 

$2k total cost of what I have

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Thats about close to what I spent in the Mundorfs.
For $2k
you can get a pair of Neo High Sens AC1A’s from Voxativ.

barely noticeable improvement, this crossover upgrade transformed the Moabs to a whole new level, night and day.

I was hoping the new Mundorf high priced caps would have transformed my Millennium tweets into something VERY XXP.
But sadly onlya  miniscule nunace = wasteful experiemnt, Now on the woofers, yes, there I got more than a  nunace. 
But sadly all the oney I put into new high tech xovers should have gone into my High sens driver purchase.
Now i am behind that budget some $1200++
Maybe you can tell your mids/highs are now more than a  nuance superior, while others listening o your new xovers may say 
*eh, well...i guess...*
To others thinking upgrading xovers is going to make your speakers into some all new, you are going down the wrong path,. Save your cash, go xover-less high sens.
based on a  painful experiement. 
Even Troels with all Z caps = xovers cost more than the drivers,,!!!!!...
Can not match a  high sens performance in mids/highs.