What do you mean by "sync my E-Synth to Cubase VST/Cakewalk/Sonic Foundry"?

If you're trying to record it digitally, you'll need the D/WAM board which has AES/EBU i/o on it. You cannot directly connect it to your s/pdif i/o but I think that there is a switch in EOS which allows you to switch the signal to s/pdif and then you only need a custom s/pdif cable (75 ohm) with rca on one end and XLR on the other.

If you simply want to record it using the analog outputs, all you need to do is connect 4 of the E-Synth outs to the 4 ins of the Delta card and record.