design.txt

OSC_IN clock
OSC_OUT clock
NRST reset button
PC0-PC7 DAC
PA8     OTG_FS_SOF
PA10    OTG_FS_ID
PA11    OTG_FS_DM
PA12    OTG_FS_DP
PB13    SPI2_SCK
PB14    SPI2_MISO
PB15    SPI2_MOSI
PA8     to SP CS (no alt func)
BOOT0 to boot button
PB6     USART1_TX
PB7     USART1_RX

proposed
PA4     DAC_OUT1
PA5     DAC_OUT2 (alternate or left channel)

Resistor ladder from notebook

Audio DAC audio filter formed by 1K in series then 10 nF to ground at signal out