…Xerex in general.  First a few notes regarding punctuation:

Sherry:

Anyone who speaks English, probably knows how to pronounce the word ‘Sherry.’  In all likelihood, many of us are likely to actually know someone named Sherry, Sheri, or Cheri, or some some other spelling most likely pronounced the same way, i.e. ‘Sherry.’  Plus most speakers of English have heard the word; and, even if they haven’t tasted it, they know that it is some kind of drink that contains alcohol; although some people think it might be a cordial or liqueur, rather than a type of fortified wine.

Jerez:

The more modern name for the region.   Pronounced with the ‘J’ sounding like an open ch with the tongue rather more contacting the palette in the back of the throat.  Many English speakers will know how this is pronounced.

Xerex:

This is rather more problematic depending on whether one is using Castillian  or Standard Spanish.  The first ‘X’ might be pronounced as the ‘J’ in Jerez, or as a ‘Shh.’ the same goes for the second ‘x’ regarding ‘shh,’ at least.  The letter ‘X’ in Spanish is used mostly in proper names or archaic words, of which Xerex is rather both.  The second ‘x,’ though not the first, might be pronounced as a ‘th’ sound.  Mind you all this comes from memory, and so may be scrambled beyond reconstitution.

I could spend a bit of time on Bing or Google researching this, however one usually ends up on a forum wherein nobody agrees with the opinion of anyone else, nobody provides an authoritative answer, and, thanks to the quality of American public education, nobody knows the difference between those two .  Time was, one could get to the bottom of a grammatical conundrum by perusing the entries in a forum.  Sadly, over the last decade or so, that has changed.  The exercise is much more likely to waste ones time rather than provide as much as a clue to any useful information.

In any case, I think it likely that it may have been pronounced ‘Sherresh,’ or ‘Sherreth;’ the first, being the pronunciation that gave rise to the English word, spelled and pronunced ‘Sherry.’  This pronunciation is not altogether adequate for an hoary word such as ‘Xerex.’  (Mind you, I’m not even bothering with the accents here at all, and I believe both ‘e’s would have had one kind or another)

And… further trouble arises when one tries to use the word in a recitative.  Does one switch all vowels and consonants around for the pronunciation of just one word in another language, and then switch them back for the remainder of the piece?  Personally I find that approach distracting; and it has the possibility of an added detraction; that of sounding pretentious.  And again, one does not like to distract from the reading of the piece.  So I think that most reader-alouders of poetry–to use a very unpretentious term–would probably benefit from a pronunciation somewhere in the vein of  ‘Herez,’ using completely ‘English normal’ vowels and consonants.  This gets across the idea that one is reading a word, older than the word ‘Sherry,’ yet preserves  the flow of English vowels and consonants contained in the rest of the piece.

But… that’s just my opinion; I could be wrong, as Dennis Miller often postulates.