The SegaCD not only added a CD drive.

It added:

1 Processor (same as the genesis, but higher speed)
6 Mbits of RAM
1 Graphic Processor
10 extra audio channels via an extra SPU.


Even with that, I think emulation can be possible (the PSP has 2 main processors!)

Also, if neogeo can be emulated, SegaCD should be easy.