No offense at all dude! It's preamps, not personal! One of my motivations for the BQC was that midrange flexibility and to be completely honest: price and ease of installation. I gave up on the "smadder setup" a while ago because the BTS system and the EXB circuit were just too hot ALL THE TIME and I was constantly clipping the input on my amp. I'd still use that in a Jazz bass (and have to great success), but not a Spector. The BQC however... It definitely is a more "clinical" sounding pre compared to the Aggies and the Spector 9v and 18v pres, though very flexible because of the midrange sweep and treble points.
The Aggies are warmer and ever since you pointed out that the OBP-3 was a combination of FET and OpAmps, I've been VERY, VERY curious to give that a whirl, esp at 18v. But as I only have two basses, and that's all I plan on having (the third "rescue bass" SSD Czech with the rare Czech 9v copy is eventually going to go to Donny, so I don't count that one), I am basically waiting to get a US 9v to put in the white "Chris" bass. I already have an 18v US in the matte black Euro 5 LX (along with DCs) and it's a dream. The 9v on a 4 string NS-2 style Spector (be it US or Euro) is my dream tone, so I am basically waiting for that. The BQC makes a high quality, affordable "in the meantime" pre amp, if that makes sense. If I had a 3rd Spector NS-2 type model (Forte or Euro), I'd be sorely tempted to try the OBP-3 at 18v. The BQC doesn't have the bark or growl, though you can cop a bit of it with the sweepable mids. But nothing (IMO) is ever going to beat the USA 9v and 18v circuits matched with EMGs and placed in a Spector. That's my dream tone and I am just one pre amp away from having it!!
But if you can't afford the Spector pre's and want something that gets closer to it, I think Patrick is dead on about the OBP-3 and 2 at 18v. I'd go for the 3 so that you get some midrange control. It's not the cheapest thing out there, but it's still way more affordable than the US 9v. And Aggies sound great in Spectors (with the exception of the OBP-1 - that is one pre amp I have never liked in any bass I've tried it in. Ugh).
But if you are just biding your time till you can get a US circuit (as I am doing) the BQC is a smaller investment than an Aggie and you can move them quickly and easily on the used market once your US circuit arrives (and you find yourself locked in your room playing your bass for two days straight

- the US circuits are that good).
But the BQC does have a lot of sweet spots to it, it's just a drier tone profile. That make sense Patrick? I know you've heard all of these at one point or another...
I just wish I could get the TP to work right for me. I understand the design and understand the controls and the best way to manipulate them, but I can never get the tone I want from them. And I'm far from an audiophile, which may be the problem. But I definitely envy the folks who use TPs as their pres and have figured out their sweet spots. I've just never had success, which certainly by no means is indicative of all the Spector players out there who have.
But man, conversations like this kick ass, don't they? I learn so much every time.