That's the trickiest aspect. They work well in print for me, because "x" and "y" are the canonical letters used to represent unknowns in many mathematical contexts. But looking at how an initial "x" is pronounced in languages that use it gets to "z", which makes it sound like the "ze/zer/zers/zerself" family, and "sh" or "h", which confuses it with the normative pronouns.

The one I'm working with is the proper sound one hears for the Greek "chi" or the German "ch": a sound that isn't quite "kh", but starts with a softer sound than "k". Interestingly, that is the sound that the International Phonetic Alphabet represents as "x". So it would fit nicely. Continuing the IPA theme, I'm working using "eh" -- as found in many languages that haven't had the vowel shift English has for their "e" symbol. So, sort of "kheh"/"kheer"/"kheers"/"kheerself", with the appropriate adjustment to the "kh" part.

Someone else I talked with about this mentioned "zh" as a possible sound for the "x". It's certainly easier to say, so it might carry the day for me.

But, as I described elsewhere, unless my gender is actually germane to what's being discussed, "them"/"their"/"theirs"/"thenmself" avoids bringing in somewhere it doesn't really belong, and therefore suits me fine.