fishbone, Since you are asking for a "to an optical" I have to assume (yikes) that you don't have a mini 3.5mm input on your preamp.
Therefore, I gather that you are trying to use the 3.5mm output of the AE and the optical input on your Preamp. If yes, then read on.... The good thing is that the 3.5mm output on the AE is in fact an optical output. What you need is a small adaptor that fits over the end of a standard TOSlink cable to allow you to connect it to the AE.
Or Some cables from monoprice have mini-toslink to standard toslink which would not need the adapter.
If you are trying to do this with a high-end glass TOSlink I don't have info on that.