I can't tell the difference


I have a primate I21 integrated amp, bowers and wilkins cm5 speakers, and a slim devices squeezebox. I recently purchased a musialcal fidelity v-dac thinking the squeezebox's dac might be my weak spot. I've done a blind comparison between the sb3's dac and the v-dac but I can't tell the difference between the two.

I really thought that the v-dac should have been a significant upgrade seeing as how it costs the same as the sb3 which has a lesser burr-brown chip and a ton of other componets where with the v-dac you are just paying for the dac and nothing else.

Should I be able to hear the difference here? How much do I need to spend to upgrade my source?
mustard
@Jult52 -- I was using an audioquest optilink-A and audioquest sidewinder RCAs with the v-dac. During the blind test I had a bargain bin RCA cable from the sb3 to the amp.
@jult52, could you point me to some documentation that describes how a cable could impact the spdif transmission? I'm no expert on the spdif protocol, but if it is anything like the TCP network protocol, there will be integrity checks built in on the sending and receiving side (transport and dac) that go a very long way to make sure what is sent is what is received. I'm very sceptical of the idea you could tell the difference between 2 properly functioning cables used for spdif transmission.
@jult52, I suppose the comparison to tcp isn't too valid as spdif won't be a two-way handshake. However, I'm still skeptical. In order for there to be a transmission error in the digital domain, the physical medium must be modified beyond a given threshold (voltage level or light measurement?) to have any impact. Yes it's technically possible, but if it's happening with any regularity I imagine the results would be painfully obvious, in which case you'd deem the cable defective. Using an optical cable would avoid the potential for surrounding electronics to impact the transmission, but based on error rates I've read in passing this likely does not matter either.
mustard...you are going to get yourself in trouble trying to apply logic to all of this! the "believe your ears" thing you have going with the blind tests is really the only way to evaluate this effectively. spdif cables will sound dramatically different, whether they should or not i don't know but they will. i actually would say that a digital cable can be the most influential cable in a system. i took great care in selecting mine and it has paid off nicely. i am graced with ignorance so i have little choice but to just give this stuff a listen.
@Richard_stacy -- I agree our ears are the end-all-be-all. However, the laws of physics cannot be evaded. There has to be some logic to where we look for differences, no?

Have you done any blind tests with your digital interconnects? I'm very open to the possibility that I'm wrong here, but I'm one of those people that needs to understand why something works... maybe I'm in the wrong hobby :)