Millers played a huge role in my (classical) musical education in the 60s and 70s. I went to school in Cambridge and visited the shop frequently. For over 30 years (I estimate) the Classical Department was managed by "Chris", whose musical preferences moulded mine until I became sufficiently confident to start arguing with him. For mainstream orchestral music his first recommendation was usually Karajan, and if Karajan hadn't recorded the piece then any DGG recording (yes, two G's in those days) would get his vote.
My memory is hazy but I think the shop moved from Sidney Street to Market Passage for a while, before moving to its current site on the corner of Sussex Street and King Street. Millers sold recorded music, sheet music and instruments, and (again, iirc) for a while the instrument part was sold to / handled by(?) another company called Ken Stevens, which had/has a separate shop, also in Sussex Street. Afaik, Millers no longer sells recorded music.
I well remember sampling many LPs in the listening booths, some of which (in the Classical Department) were fully enclosed cubicles with loudspeakers, and a bench seat that could accommodate two listeners at a pinch. The company also had a neat idea to encourage present-giving: if you told them that the LP was to be a gift, they would glue a paper seal to the inside of the LP sleeve which would have to be cut or torn in order to remove and play the disc - clever eh?
Millers Music shop 12 Sussex Street King Street 6 & &Sidney Street Cambrigde