Thanks Mica!
Sorry guys, I'm a bit behind.
That Essence was my first Alembic. I bought it used. A previous owner installed the middle pickup. It was not a professional installation; someone routed a pickup cavity and screwed it in there, then they unplugged the neck pickup and plugged in the new middle pickup. That was it.
This was my main bass for a long time. Although I liked the combination of the middle and bridge pickups, I unplugged the middle pickup and plugged the neck pickup back in. After thinking about it for a long time, I finally picked up a Spoiler as a replacement and sent my Essence to Santa Rosa.
Alembic reinstalled the middle pickup properly. And in addition to a three way Q switch, they installed a pickup selector switch. I also got a satin feel neck, aluminum side position markers, and brass sustain block and had the frets crowned.
While waiting for the Essence, I picked up the S1 that Jim mentioned above and that became my main bass. Thus I haven't used the Essence much plugged in. It has been my main practice bass (unplugged) just because it is so much fun to play; I love the neck. But I dont' plug it in to my main rig, because it would require a substantial re-Eq of everything; my rig is setup for my S1. I do really like the addition of the Q switch, and I find that on this bass I seem to prefer the switch in the off position, although on my S1 the bridge Q is always on high.
Because it's all Maple, this bass was a bit aggressive to begin with. Adding the sustain block makes it more so. What (comparatively)little I've experimented with it suggests that the pickup combinations and Q choices are all variations on the aggression theme. So far it appears that my favorite pickup combo is middle and bridge. And I've noticed that I'm making more use of the Pan control than I used to. But again, I haven't EQ'd my rig to match the bass. If I were running this bass through my F-1X and SF-2, I could probably tone down the aggressiveness, warm up the low end and smooth out the high end and make much better uses of the all the available tone combinations.
So, the changes made a wonderful bass much more flexible. But with the S1 getting all the work, the Essence isn't getting the attention that it deserves.