RCA or Optical?

Does not matter if working properly.
Mapman

Does not matter? The audiophile police are watching you.

I've used both over the years and NEVER been able to tell the difference.

I've used both on half a dozen Dacs and have found even a cheap RCA sounds better than a big-buck optical.

I recently reconfigured my system and came up short with my vintage Audioquest RCA (true 75 ohm) digital cable.
I substituted a generic Toslink and thought there was substantial improvement. I purchased a glass fiber Wireworld Toslink. I like it but can't get it to pass 24/192 data to a Rega DAC (it's 3 meters long BTW).

I've had well over 50 DACs in my system over the past 4-5 years.

I have never heard an optical (toslink) connection that even comes close to what a coax can do. Nor a coax over what an AES/EBU can do. Nor what a I2S or Firewire can do over the AES/EBU. Although very few devices have I2S or Firewire connections, but the ones that do are superb.

My order of preference:

1. I2S or Firewire
2. AES/EBU
3. Coax (BNC)
4. Coax (RCA)
5. AT&T Glass Fiber
6. Toslink

Just my opinion...