Thanks tubeperson.  Much appreciated.  I think I want the tone I keep hearing here at the club.  Almost like a vintage acoustic guitar in the upper registers, but silky down low.  Would that be low gauge, low tension?  thanks again
 
I'm a severe Stanley fan too, btw.

No wonder some folks go for graphite necks but for me you cannot beat the look of wood!
Oh 2000th post!!!!

Terryc -  that's a ton of fun at the club for you!  Congrats

Thanks again for all helpful tips! I will try to find strings with heavier tension. If that fails I might consider a heat bend, but I live in Norway and don't know if it possible to have it done locally.
 
Cheers,
Atle

Another thing you might try is to loosen the truss rods fully. Insert something rigid but soft outside  between the strings and fretboard and over tighten the strings. Let it sit this way for a week or two slightly tightening the strings over the time. After the couple of weeks snug the truss rod nuts up and remove whatever you used between the strings and neck. After this try adjusting the relief to where you would like to see it.    
 
I have done this once before and it reset the neck enough to get the relief where I wanted it to be. Again it does take a day or so for the relief to settle in when the truss rod is loosened.  
 
Keith

When Alembic made your bass, they set it up for the environmental conditions and wood conditions at that time.  Each piece of wood is different, so each neck's neutral condition (no strings on) will be different.  When it's strung up and relief is set, they do whatever what's needed to hit the factory target for action.  
 
But your climate and desired action may not be in the range where you can adjust to what you need using the truss rod.  
 
I think the next thing you should do is find a good tech to take a look at the frets.  Sometimes there might be some unevenness in the neck or frets that's causing your buzz.  Your bass didn't have this problem when it came out of the factory, but can be the result of wear, wood shifting, or imprecise prior fret work.  This kind of buzz is more likely to show up with light strings and low action (although I don't think you're target action is all that low) and the truss rod won't adjust it out.  
 
Another thing that a good shop can do is to use a neck jig to force a little more relief into the neck, then tap the neck to see if the they can get the truss rod to shift a little (this works on guitars, unlikely they will have the right jig for a through-body bass!).  They use a jig like this and a heat blanket to do the heat bend.
 
If you have a lot of fret height, a good tech can also mill some relief into the tops of the frets, regardless of the shape of the wood.  This can be very effective for eliminating buzz when you want a very flat neck.
 
A bunch of stuff to try!  I'd definitely pay a visit to a good tech first to see whether the problem can be solved in the frets.
 
David Fung

Can an identical replacement set of strings have greater tension than the set it replaced?  My recent experience suggests.. yes!  Anyone have a similar experience?

Dan; did you remove all of the old strings before putting the new ones on, or did you replace one string at a time?

Good question!  In fact, as opposed to the way I usually do it, I removed them all at once, oiled the ebony fingerboard, then re-strung the whole 5-string.

Are you noticing a change in the neck relief, or can you feel a difference by playing it? If the former, it could just mean that you need to do a (quick?) setup.
 
Or, maybe the formula for the strings changed in the interim between? Seems much less likely. Are you sure they are absolutely identical gauges?

Yes, they're absolutely identical gauges, same CX-3 strings, everything!  The tension on the new set resulted in much higher action at the 12th fret, I increased tension on both truss rods, which lowered the action back to where it was, but then I began to think...why did this happen?

While it was a year or two back I had the opposite case where I put on a new set of CX3's and didn't have enough relief. I asked Mica at that time if they had changed anything to give the strings less tension and she said nothing had changed. It hasn't done it since then so I just assume it was coincidence that the bass needed adjusting at the same time I changed strings.  
 
Keith

Thanks for all your input, everyone.  It's certainly no biggie.  I was just curious.  The tension on the truss rods, when I went to tighten, seemed looser than I remember, so what may have happened was, when I removed all the strings, somehow the neck breathed a sigh of relief... who knows?  It also may have to do with the relative humidity (low) right now.

By the way, it's an '09 MK, relatively new... so it wouldn't surprise me if things were still settling in a bit.