Artificial languages generally do not or should not have unusual sounds, which might be defines as "any sound not in Hawaiian". Klingon does, but it's not clear to what extend users execute the standard correctly. Paid actors seem to have a few skills in that realm, but really it's not reasonable to create a standard that is too difficult for most people to produce. That said, it sounds like you're describing [χ], a voiceless uvular fricative, which although it is a sound not in English, people are not too bad at pronouncing. It doesn't exist in German, but English speakers faking German often produce [χ] for
But really, really, really, you should provide actual recorded models. Record a "native speaker" saying "macxma" so that interested people can hear what it actually is. All production is based on hearing, and not technical description. (I used to teach this point by instructing students on how to articulate ejective [p'], which almost nobody could do based on knowledge of how to contract muscles, and virtually everybody could do once they hear an example).
At least, it sounds as though you are describing a sound that you intend for a conlang. OTOH it also sounds like you are basing this on a sound of a language that you heard (what language? any clue?). Since you thought that [χ] and [ʜ] are the two closest sounds, based on that one webpage, let me up the ante for you. I recommend John Esling's page at
https://web.uvic.ca/ling/resources/ipa/charts/IPAlab/IPAlab.htm. He is in fact the world's leading expert on phonetics of back of the mouth sounds. One thing that you should understand is that those recorded performances are not from real language, they are theoretical constructs. The consonants [ʕ, ħ] in languages that have them, like Arabic, don't sound the same as the IPA models, but they are more like those performances than e.g. [γ] or [ɢ].
You might then decide that the sound you heard was [ʜ] – possible if you heard it from a Somali speaker. Can you make that sound correctly, can you teach others to make it correctly? I am skeptical. I think you have the best changes of success with [χ]. If you've settled on [χ] as your realistically-achievable target, "kx" seems like a possible spelling, and no matter what you do, somebody is going to revert to English orthographic practices. (Anecdote: the language has aspirated and unaspirated consonants, spelled p vs. ph, t vs th. When I sat in on Zulu, for two weeks they only spoke and did not write, then they introduced spelling. Suddenly people were pronouncing [tʰ] as [θ], and the lateral click as "ks" 'cuz it's spelled "x").
The main point is that you should try to promulgate recorded samples, which is easy if you have a web page.