Who are the most underground high-end companies

i've a few for you Taters:
Selah Audio in NC - you hear a little about them now & then. They make very good sound line-array speakers & the owner is a very good person to talk to.
Moon Audio - Drew Baird runs this operation from Raleigh/Durham area. Very good & cost effective cables (atlas they used to be inexpensive. Don't know if he's raised his prices a lot)
Green Mountain Audio in Colorado Springs - my favorite cone-driver speaker manuf. I've owned his speakers & my brother still does. Like someone wrote earlier. I'm not on his payroll - just an enthusiastic supporter of his really good sounding speakers, One of the very few speakers that are time-coherent, which is the only way to go.
K & K Audio - which is run by Kevin Carter. His best selling product has been his phono stage. Very little spoken about him though he does have a forum over on Audio Asylum. Really nice fellow to deal with - calls a spade, a spade & very knowledgable. 

a few auto-correct typos - please excuse.

good to see that a few others mentioned Green Mtn Audio - I 2nd.

Also, 2nd Scott Nixon - I’ve his non-oversampling DAC in my bedroom system that uses the Philips TDA1541/43 chipset. Excellent sonics. I think that he still makes new tube DACs.

 Peter with PBN Audio,should be mentioned, in the San Diego area, he is always striving to make his products better and his customer service is off the charts. Enjoy the Music

+2 for Selah Audio, excellent speakers, well designed and very reasonably priced for the level of performance that they provide. Not to mention that Rick, is easy to work with and will design any speaker that fits your needs. Yes I do own them as well.

Quicksilver is a good example of a great company that doesn't advertise.... I have a pair of Mid Mono amps which are a huge bang for the buck.    I love those amps......