Thanks all for your replies.
I did contact Simaudio and therii opinion was that
while there should be no difference (i.e. if using their gear) there MAY be a small improvements to be had.using the XLR cables.
Since no one was overly enamoured with the Shiit products and since the Simaudio Moon contact does not believe there would be a significant improvement by using XLR cables, I have decided not to proceed.
The single ended cables I currently have are excellent performers
- and building a set of XLR cables just to satisfy my own curiosity would take away funds from other possible "projects"
Thanks to all that posted - much appreciated
Regads - Steve