i would say two discs because there is probably something in the disc that says, "okay no more data, input next disc."
i say this because from the stuff i, ahem, legally download, the cds come as they are, eg 2 cds = 2 separate isos. like for need for speed, there were 4 separate isos and each time one is finished, it would as for the next and i would just emulate the next.
i hope this helps.