I have a Transporter (as well as 3 Duet's) and the Transporter is a great piece of kit. There is still nothing that does what it can years after its release.
First, it's more versatile than other solutions because it has more inputs. With the streamer to DAC route you are already using up one digital input for streamed music. The Transporter converts the music internally, so you still have all the digital inputs to use for other devices such as PVR and DVD player.
It has both balanced and single ended outputs which not all other DAC's have.
The volume control is digital attenuation, which I'm pretty sure is the same method that W4S uses. The single ended outputs of the Transporter have jumpers that can be set though to match your power amp if you do want to use it as a pre-amp. The jumpers don't affect the balanced outs.
Another good thing about the Transporter is it's resolution. Stereophile measured almost 20 bits of resolution, which is still pretty much state of the art performance, so you can attenuate its output quite a bit before it becomes audible. It's other measurements are also superb.
You can also control the Transporter with either wi-fi or IR. You can control it with your smartphone, the supplied remote, your computer/iPad or your learning remote. I have it programmed into my Harmony One so that when I choose an activity the Transporter automatically selects the right input for the desired activity.
It also reduces the box and cable count by combining the transport and DAC into one, and the display is a nice bonus that no other DAC can match.
If that wasn't enough, it also sounds pretty good too.
