The output from a CD-ROM is a straight bitstream at 5V TTL level, not S/PDIF 1Vpp level. Interfacing it to the coaxial is simple enough, though.
Some other problems you might find are: Not all CDROM's activate the digital output at all; often, the output is continuous and may have spikes, there may be problems synchronising the signal at the start of a track with a DAC
Then again, it may work perfectly, once the signal level is adjusted.