Trish,
To follow this up now you have his Regimental Number you will have to subscribe to either Ancestry or Find my Past, or get someone to do a look-up for you, or try the South Wales Boarderers museum in Brecon again.
I see from your family tree info that you too have Dix interest. My wifes mother Betty was a Dix from the line of Jonah (1838-1888) who came up from Somerset and settled in Landavel, Cwm, Ebbw Vale and James (1869-1936), and Jonah (1892-1949) who moved to Argoed, Blackwood.
Is this the same line as yours?
Gerry