Steve,
If you buy an off-the-shelf AES/EBU transceiver, TI and Cirrus Logic both make them IIRC, it will be optimised for 110 Ohm for sure.
If you take the SPDIF output from your DSP chip and put it through a pair of inverting and non-inverting amplifiers, you can drive whatever impedance cable you want.

Mark
G68, baby Genelecs, Humax Foxsat, Oppo+Vanity93, Toshiba HD-A35, Pioneer CLD-925 + Meridian 519, various other random bits and bobs
Got a black G08.2 you want to sell?