Yes, I remember A1 Music from the late '70's . Could never afford anything there, but I remember you went down the stairs and there was a huge cavernous shop underneath which went all the way under Oxford St.
Also in Oxford street a few doors up the road (past the Salisbury and Oxford Rd Station) there were a couple of music shops, one of which sold Wal basses.
My favourites from that time were both next door to one another on Chester Rd, next to a dodgy pub with a pool table. They were Muir Music, owned by Geoff Muir. They sold electric guitars, drums and PA. Dave Lunt was the amp repair guy who worked there.
Next door was Sounds Acoustic, run by Charlie Carter and his friend Graham. They sold acoustic guitars,mandolins and banjos. I spent a lot of time there and still have a Fylde Orsino which I bought second hand from them, hire purchase £10 a month!