Mike, In my system, the Aural Symphonics Optimism V2 fiber gives a less digital sound (less bright and less mechanical). It also gives better depth, more details and texture of instrument and voices. Overall, the emmlabs stock optical fiber sounded a bit muddy relative to the Optimism especially the bass.
I don't know the exact spec of the Optimism, nor the stock fibers. However, in the emmlabs DCC2 manual, it stated the ST fiber has to be multi-mode. I'm pretty sure the Optimism is multi-mode. But there can be 2 sizes: 50 micron core and 62.5 micron core. They both use the same ST connector. Though the later size is the more commonly used.
You might want to verify with Ed Meitner again if you are skeptical about compatibility.
As far as I remember, through The Cable Company, you can try it for 30 days (less shipping days) and return it if it doesn't work for your setup. The most you can loss is the shipping fee.
