Two messengers between the gods and humans were two gods, both from Greek mythology, Hermes and Iris. Both were gods who went between the world of the gods (music) and the humans (physical ear). Both names could be used, one for the -12dB and for the -24dB, or Iris (or possibly iRis) could be used for both. Iris was the personification of a rainbow, which is physically reminiscent of the shape of the attenuator. Both Hermes and Iris carried a winged staff called the caduceus, which could be used in marketing.
Gemini and Mercury, other iFi product names, are Roman though. The Roman version of Iris is Arcus. There is a lot to like about calling the attenuator Arcus. Like Iris, she is the messenger of the gods and is also associated with rainbows. She moves fast and thus delivers messages well. In Latin, arcus can mean arc, bow, rainbow (again, terms which resemble the physical shape of the attenuator). I think this is my best idea, both capturing the function and shape of the attenuator while also integrating it into the iFi product line of accessories.
In a different direction, I've thought some of the difficulty is that an attenuator does something that sounds negative. Who wants less power? Who wants to reduce? It takes too much explanation. Something positive though is defending/guarding. This is about volume control and, while predominantly about sound quality for headfiers, is also about volume. What about Cerberus, the three-headed dog who guarded the underworld? (He had a serpent tail, reminding me of the looks of the attenuator.) Other less creative ideas are iDefender, iGuardian, etc.
Another idea, which rides off of Thor's popularity in the Marvel universe of movies, is Bifrost. Bifrost is the rainbow bridge that connects the world of the humans (Midgard) to the world of the gods (Asgard). In this picture your amps, are the world of the gods but it needs a bridge to the world of humans. There is so much cool marketing that could be done with this idea, I think. (But...as I remember, this is the name of a Schiit product already...)
Gain Composure (I think this is a really cool idea. It takes a well-known phrase and gives it a whole new, and at the same time accurate, meaning.)
iFocus
iHarness
iBridle
iCompose
Composer (Compose with a play on words)
Composure
(All could be in two versions -12dB, -24dB)