Man, I'm sorry. I completely misunderstood your question.
I won't pretend to understand things like jitter and such, which, from what I understand, have a vast impact on sound quality. I also do not have any sort of dock for an iPod and have never used one as a streaming device.
If you do any sort of research here on audiogon, you will see that there are many, including those at Wyred4Sound and Empirical Audio (I believe), who praise the Sonos for its simplicity of operation, but also criticize it's performance. There are mods and adds ons out there that some say are required to get audiophile quality out of a Sonos.
Now, that having been said, I have a Sonos that pulls its files off of a NAS (2TB or storage). I also have a Squeezebox touch because it's capable of doing hi def files greater than 16/48. Although I do, admittedly, have a very modest system (NAD 162 Pre, Aragon 2004 Amp and Paradigm speakers), I think that the Sonos sounds great. Maybe it's because my system just isn't good enough for me to be able to tell the difference. Perhaps I just happen to fall into the category of ignorance being bliss. I don't even have a CD player any longer. All of my music is streamed.
Considering your situation, I think I'd have to say that I see no reason why a Sonos would sound any better or worse than what you're running now, assuming like music files whether from ripped CDs or MOG.
The only advantage that I would see to the Sonos is it's ability to pull files from a server giving you almost infinite storage.
Since this is just for a secondary system, you may also want to consider an AppleTV. The only drawback being that it needs a computer to draw files through. My AppleTV pulls files from one of the computers that I have, which in turn pull the music from the NAS. I don't use the AppleTV much, though.
On a last note, I don't regret getting the Sonos for one second. It's rock solid, meaning that I've never had a problem with it. I wish that I could say the same thing about the Squeezebox. People love the Sonos when I have parties. I just put the iPad out on a table with the MOG app running and it's like a juke box. I just enable the volume control on the Sonos and limit the volume with the knob on the preamp and shut the doors to the cabinet. With this setup, everyone has a controller.
Sorry about the verbal vomit, but I do really like the Sonos unit. I just wish that I could have offered you more of an A/B comparison.