computer audio question

Different DACs can sound very different. How different will depend on what DAC you are using and what replacement you are getting.

Different software players can sound different too and in some cases, they sound more different from one another than different DACs do.

Changing a DAC is akin to changing a cartridge. As Sidssp implied, do not discount the transport aspects too. There has been great strides made in that arena through the use of computers as the digital transport mechanism including the player software and file types.

There's been much progress in DAC and DAC chips design since The Bel Canto DAC 2 came out almost 10 years ago.

That said, Your most cost-effective upgrade at this point could be to add something like the M2Tech Hiface USB/SPDIF converter and output your computer's bitstream data through a USB port. This isolates your computer RFI/EMI from the DAC, helps control jitter, and has other benefits which all should help your source sound more musical.

As others noted above, it all begins with a good lossless audio file being output from one of many good software packages such as Foobar or JRiver for PC, or ITunes for the Mac.

The DAC should make a noticeable difference similar to changing phono carts as noted or even simialr to changing players with built in dacs.. If not, then the system may just not be very resolving or revealing to start.