Try this:

mov a,WMCON
clr acc.2 ; Set first dptr 0
mov WMCON,a
mov dptr,#SoundAddr ; sound adr to be used later
mov a,WMCON
setb acc.2 ; select DPTR1
mov WMCON,a
mov a,#PWRUP ; start ISD4002 device
call write_spi_byte ; write it to SPI device (will disturb DPTR)
mov a,WMCON
clr acc.2 ; back to DPTR0
mov WMCON,a