Hi Jake, I know who you are, we communicated via email regarding the Spirits in Chicago if you remember.
I have driven the Spirits with many powerful amps and yes, they benefit from current. The best sound I got out of them was with 200W class A Jadis JA200 MKii tube monos (you can see them sitting next to the 845NEC) and the Gryphon Antileon Evo which is 150W class A solid state. I was just pleasantly surprised that those 845NEC were able to get a reasonable bass and rather relaxed midrange and treble out of the Spirits. Although, they would not be my absolute first choice top drive them.
The Spirits are different from the other Vivid Giyas, as the bass drivers have much larger motor systems - a full 5 inch coil sitting in a dense neodymium magnet system. Plus the x-max of the driver has been increased by 50%. All in all a supreme bass driver - and there are two of them in each cab. So you can imagine the impedance is on the lowish side, hence a strong amplifier is required. But when you get that right amp, the bass is heaven, and extremely extended to 16 hz and below with the power to match.