The Ethernet is present on F1, F2, F4, F7 and H7. F1 is probably the cheapest, but also the oldest and least recommended. For 8 audio channels I highly recommend using SAI peripheral(s), not SPI/I2S. SAI is present starting from F4 (and up). Most likely you will use either TDM mode or 4 x I2S lines. For the latter case you need 2 instances of SAI peripherals. Yes 2, because each of them has 2 separate streams. For 2 SAI peripherals you need at least F7.