Most everyone has some sort of inner voice when they read, it's not creepy at all, I understand what you mean completely. I thought about doing /æ/ for AntiExtremes, but I think it might cause some serious technical issues I'd rather avoid because it might have trouble interpreting the symbol on certain systems. Plus it's very hard to type, which is just annoying for the end user.

I think /x/ is kind of cool, it reminds me of 'x marks the spot' or 'Mr. X' (did you see that Simpsons episode?) or the 'x-files'. Has a kind of mystery about it, and I think that's catchy. Also a lot easier to remember than most other letters. Plus x is the default variable in math, in which you can put anything. So it works all those ways! :)