I did it awhile ago. It does make a big difference. The DAC in the SNES sucks. I've also done it to my Saturn and plan to do it to my DC. Why would you take the digital stream and put it through a cheap ass eBay DAC, and not at least directly to your receiver?
What would really be something is if you could do it to the N64. The problem there is that the N64 does not output standard sample rates, so you'd have to put your own clock on it. If I knew more about Digital Audio I would do it.
This reminds me of a caveat about the SNES. The SNES outputs a 31.5 khz signal. The standards are 32 khz, 44.1 khz, 48 khz, 92 khz, and 192 khz. Because the SNES signal isn't perfectly 32 khz, it may
not work with all DACs. I haven't run into one yet, but I've heard tale of DACs that it won't work with.