The xISO would be split up in all these RAR archives and upon extracting the xISO in xISO xFER, I would have to find in which RAR acrhive the current file (in the xISO) is, where in that particular RAR archive it resides and then extract the RAR archive, then the file from that xISO chunk.
As far as I know, you cannot extract specific RAR files (R00, R01/part01, part02...).
If that isn't possible, one would have to extract all RAR files until you hit the correct RAR part file, check if it spans over multiple part files, abort RAR extraction, create any eventual directory trees where the file should be extracted (if not already exists), extract the file from the xISO chunk, delete the xISO chunk, and start all over again.
So, as you might understand, not only is it not worthwhile, it is simply not the optimal condition for xISO xFER to work in (regarding speed and so on...).
I think you would go back to use WinRAR to extract the xISO image and then use xISO xFER, or any ISO tool of your choice to extract the files.