Нашел
Тут говориться про момент из его бигорафии, когда он решил взять себе ник "Tech N9ne" :

He and his buddy paged through a book of guns and ammo, but none of the words he saw seemed quite killer enough to him. " 'AK47!' I'm like, no. 'Uzi.' No! '12 gauge!' No," recalls Yates, now 36 and better known in the underground rap game as Tech N9ne. "We got to the end of the book, and it was like, 'Man we ain't find nothing.' But there was a picture of a Tec-9 at the back. He said Tec-9 because the way you rap is like fast, like 'tekatekateka' -- fully automatic."

The name stuck. And it turned out to have significance to Yates because it was worthy of the rhymes he was throwing and the varied beats he found attractive. Tech N9ne has tried on dozens of different styles over the years, wandering from rat-a-tat deliveries to slower rhythms over leisurely beats.

Ну и его объяснения собственно по поводу того что для него символизирует число 9:

Tech is a man full of theories -- whether they involve using political science in the name of selling records and filling theaters, or the more mystical, unintended consequences of his chosen name. "I never thought in a million years I would get my name from a gun and it would turn from something negative into something positive," he says.

"The way we spelled it was Tech, but it's really Tec. We did Tech like short for technique. And I learned over the years that 9 is the number of completion. Nine months for a pregnancy; cat's got nine lives; the whole nine yards is everything. So my name started to make sense, like I was the complete technique of rhyme. I'm every MC in one. It fits me perfectly because I'm ambidextrous. I'm everywhere. I'm sizzling all types of styles, not just one."