TeX being from τέχνη make sense, I do enjoy startling people by pronouncing it thus (as Knuth recommends).

xonsh being pronounced /kɑnʃ/ and not /eks.ɑnʃ/ or /xɑnʃ/, or even /zɑnʃ/, is just one of those things I have to remember.

pronouncing TeX /tɛk/ is better than /tɛks/, but really it's /tɛx/, the way Bach is /bax/.