Hi Brumgum: I don't have any knowledge of the Royal Reserves per se. I did find this piece on line, however.
The Royal Reserve Regiments were raised from 20 February 1900 on to relieve regular battalions for the Boer War. Early 1901 these regiments reorganised into the Royal Garrison Regiment whic existed until 1906.
As for the Southern Reserve Regiment, here is a summary:
Royal Southern Reserve Regiment
Formed 1900 with two bns. Disb by late 1901.
1st Bn
Formed 16 Mar. 1900 at Portsmouth. Disb later.
2nd Bn
Formed 12 May 1900 at Portsmouth. Disb later.