I’ve had decent results using a strip board LM386 amp on the input stage of the tank , and then going ¼”out to an amp or interface.
Input (¼” or whatever you want to use) -> LM386 -> tank -> ¼” out -> interface, amp , etc.
You can also add another LM386 on the output side to heat things up and still get away with using a single 9 volt.
This circuit will take between 4 to 15 volts, so no issues powering two of them. When going this route, I ended up adding a trimpot to the output amp to keep things in check. It's fairly loud without it.
LM386 schematic I used:
mind the cuts or breaks in the stripboard (red squares w/circles)
I haven’t experimented with this yet, but adding a tone control would be nice. It’s simple enough to build, and no power needed. You could actually just build this on a pot, eliminating the need for another board.
Keep in mind, the LM386 is almost a utility type amp. A lot of hardcore audiophile types might thumb their nose at it. It doesn’t sound bad or anything, but there are better ones. It’s just simple enough to get one's head around, all the parts are completely off the shelf, and it sounds decent. In my case, there was no matching of impedance or anything. A little caveman-ish but it’s still effective.
I’ve heard good things about FET amps, but haven’t built any. They look simple enough though.
http://www.till.com/articles/GuitarPreamp/