Despite Rcprince's knowledgable endorsement, as the owner of an InnerSound preamp, I can attest to the fact that however transparent it may be, my DAC sounds even better if I take the amp inputs from the line outs rather than the main outs, thereby bypassing the preamp's active gain and attenuation stages, and surrender all control over volume level (my DAC doesn't have that feature). You can test this with your current digital front end by setting your preamp's volume control to "79" (unity gain on this preamp - try to choose audition disks that aren't encoded at very high levels so as not to get blown away, or forget about this test entirely if you never listen at anything approaching the "79" setting), and then listening switching between the regular main outs, and moving the interconnects going to your amp over to either the monitor outs or the processor outs. This gives you the most fair comparision, because you are maintaining the same number of interconnects and I/O jacks in the circuit, thereby revealing the exact contribution of the preamp itself (it's also easier to swap the test conditions quickly this way); the difference you hear once you connect your new DAC directly to the amp and eliminate one set of IC's and jacks will tend to be even greater for their loss, but worse for the added question of your new DAC's attenuator quality, which may or may not equal the InnerSound's. Unless there's something unusual about the electrical interface of your DAC's output and your amp's input, I think you will find a surprising improvement with the preamp's guts taken out of the loop in this test.
I would encourage anybody to try this kind of test to hear just what contribution (or subtraction) your preamp is making to the sound of your digital front end, provided your preamp's unity gain setting can be determined, either through math or through trial and error, and if it has either processor loop outs or unbuffered tape outs. I posted a thread on this topic before (see my threads), but no one who responded at the time seemed to have tried this for themselves.
I would encourage anybody to try this kind of test to hear just what contribution (or subtraction) your preamp is making to the sound of your digital front end, provided your preamp's unity gain setting can be determined, either through math or through trial and error, and if it has either processor loop outs or unbuffered tape outs. I posted a thread on this topic before (see my threads), but no one who responded at the time seemed to have tried this for themselves.