I can't honestly tell you whether you'd notice the difference or not but I can give you some info that might help.
I have an 851N which is basically an updated Stream Magic 6. It uses DSP to implement the volume control rather than bit reduction (which is more likely to affect quality) and I understand the Stream Magic also does. I use it through a conventional integrated amp because I also have a record palyer so I need to be able to switch sources. The amp also has a power amp direct in. I've tried the streamer in pre-amp mode directly into the power amp, and in plain streamer mode into a pre-amp channel and I couldn't tell the difference.
So unless the volume implementation on the 851N is significantly different, I don't think you'd notice any improvement.