USB DAC Questions

[tporter]

Hi all -
I'm pretty new at this & have a couple of questions: Looking at a kit on ebay, there's a kit for a USB DAC that uses two primary IC's - a PCM2706 USBDAC & a Cirrus CS4398 DAC. Why does this kit use two DACs? I've seen this approach in other designs. Is the DAC on the PCM 2706 useless? If so, why not just use a USB streaming controller like the TAS1020B instead of the PCM2706?

Two: Ouput stage. I'd like to use the USBDAC to drive either a pair of bookshelf speakers or connect into a separate amp. There seem to be numerous ways to skin this cat. Is there a *best* way? On the output stage, people have used Butterworth, Sallen & other filters. Again, is there one that is accepted as the *best* or most commonly accepted?

Thanks for any help.

[singa]

Hi,
I'm not so familiar with PCM2706 but it could be but I don't think so that
it outputs I2S data stream that can be fed to CS4398 dac for quality playback.
Other than that it just the option to use usb or coaxial/optical datastream.
But dac in pcm2706 is inferior to cs4398.
What dac output brickwall filter is best is usually the easiest and cheapest way to impliment the filter.Even complicated ones using multiple opamps
does not give an edge quality wise so the simpler the better.That's why the
best way to improve it is to add a tube buffer to have a favourable signal
spectrum of "triode like" frequency distribution. singa