In case anybody's still interested
, I've decided to use a tube buffer/active with the Tortuga for volume control. My system is going to be active with separate amps for the tweeter, midwoofer and multiple subs. It's too complicated to use a passive pre. because it severely limits my choice of amps and sources. I guess you can divide the voltage only so many times. I fooled around with the speaker level cable, resistor implant to the Crown with mixed results and since this is for the critical midwoofer, not a sub, I'd like a more straightforward implementation.
One issue I'd like to make sure I get right is the buffer vs. active choice. Do I need an active unit because of splitting the voltage to multiple amps? The buffer adds to the current capacity but does nothing for the voltage. Definitely don't want to build a buffer and then find out I still can't power my midwoofer (AE TD15m) with the Crown or similar amp. I hope that the positive attributes of the Tortuga won't get lost with the addition of an active buffer.
It's unfortunate but I'll probably have to rebuild my nice enclosure so that there will be enough room to house the pre + the Tortuga. Fortunately, I have enough redwood to build an expanded faceplate. I'll reuse the side pieces but the top, bottom and rear panel will have to be replaced.
Now I'll have to decide which line stage to use. Dave, the Aikido kits look interesting. I'm open to suggestions as to which kit would be the most suitable for my application. The 12Vac PCB and parts kit
http://glass-ware.stores.yahoo.net/aikido12vac.html might be the simplest to implement and I could use my Astron power supply. Of course, if Tortuga comes up with a buffer I'd be interested in that too.