I have both a transporter and a squeezebox. Problem if you use the integrated volume control is that the preamp gain setting is implemented in by a digital gain setting in the DAC chip: if you output less than ~30dB below the max volume, you start losing on S?N ratio (that's why I use two passive attenuators at the input of the amp, as the amp gain is too high). Result is quite good...
On other DAC/CD players, the preamplification is done in analog domain, like in my (ordered) APL NWO 2.5T (supposed to be great, even better than the best preamp, will tell you when I receive it next month)
On other DAC/CD players, the preamplification is done in analog domain, like in my (ordered) APL NWO 2.5T (supposed to be great, even better than the best preamp, will tell you when I receive it next month)