I'm sorry, I didn't mention it was guitar heads I was looking at. I'm more than set for bass gear. f1x sf2 plx 3402 (x2) genz benz gbe 1200 ul212, t310, low b4. whappo jr plus 2 jbl mpro 18's if I lose my mind entirely.
Any suggestions on heads would be appreciated, keeping in mind all of the thoughts above on gain, tone and active pups.
(Guy in my band loves boogie mark 4's.)

There are plenty of players using guitars with active EMGs but I have never seen an amp with inputs labeled active / passive either.  
 
Kevin, I had my Strat and Starcaster (the old hollow-body kind) with me when I used the Blackstone so I can't lend insight as to how it would perform with Alembic electronics.
 
Danno, what kind of sound are you looking for? Mesa makes some really nice stuff, from clean American sounding to very agro. The Genz Benz stuff I've seen appears to be very nice quality stuff too. If you have the wallet, take a look at Two Rock. Or for a more British Plexi sound maybe a Bruno Pony 50. I would say take your guitar(s) and a decent cord to your favorite dealer and try a few things.
 
Peace
Tom

I've seen active/passive inputs on acoustic guitar amps, never on a elecric guitar amp.
 
Danno:  
 
Another vote for Boogie, but I'd think twice about a Mark IV.  To me they are overkill - just too much control, too many variables.  I played a Mark III for almost 20 years.  Last year I swithed to a Mark IIC+, the holy grail of boogies.  I like the lead tone a little more than on the Mark III.  The best lead tone, IMHO is the original Mark I, but they really don't channel switch.  You can either plug into the rhythm input, or the lead input.  I thought about setting up a two Mark I rig, but my back vetoed the idea.  Of course the Mark III and Mark IV give you the crunch rhythm channel (think Marshall) that the Mark II lacks.
 
Bill, tgo

Thanks guys. i just have to get out there and try some things out. Maybe the gas will pass and I'll pay off my Alembic bill before the bass is delivered.

I emailed Jon Blackstone, and he says he believes his OD unit should work fine as long as it is switched to buffered mode (I assume an internal setting on the pedal?).  I may give one of these a shot.

Duh, I guess I should have read his website closer:
 
There is now an internal switch that puts the pedal into buffered mode, permitting use after other effects, wireless systems and active pickups.

I picked up a Solo 50 Rectifier. Now to mess around with a tube sound!