I do not know if this is helpful since i have not owned a HIGH END streamer and cannot comment about that but...
I have a Squeezebox and I have it running into a Benchmark DAC USB1. The benchmark bypasses any preamp as it acts as it's own preamp. With this configuration I am NOT using the internal DAC of the Squeezebox, I am using the Benchmark DAC.
When compared to a high end CD player like an Arcam, Rega and a Cambridge Audio, i could hear
no difference. My files are just AIFF.
The only problem I have ever had was a drop out of sound since my Squeezbox is wireless not wired and the stream was interrupted somehow. In that sense I like a dedicated CD player.
Also I have heard good things about the LOGITECH TRANSPORTER and you could connect any external DAC you like to it. There would be many opinions here as to what DAC would sound the best. Also the file type and manner by which you digitally copy or store seems to make a big difference. I have been satisfied with AIFF which is not compressed.
I have been happy with the SB and when I did have a problem with it, it was fixed by Logitech quickly and no charge. I have upgraded the power supply via Bolder Cable and it is pretty quiet.