AirPort Express and Sonos both offer high levels of jitter, so don't expect them to be as good as a CD player without adding a reclocker or doing major mods to them, ala power and clocks. Low-jitter reclockers are available.
As for the preamp, it will ultimately hold-back your system. I would sell it and move on. The best pre to get is no pre. If you MUST have one, then get a transformer-based linestage from a good transformer company like Music First in the UK. I know the importer of this one. One scenerio that is interesting in modern DACs is a high-quality built-in volume control. Some of these are not like classical preamps or even passive linestages, they are even better. The level of clarity you get when you eliminate the pre is simply astounding.
If you want great digital sound, whether from CD player, computer or WiFi device, it all depends on the master clock. Get a source device with a really low jitter master clock first, and then deal with the preamp. This is the ONLY way to quality audio. If you start with a high-jitter source and dont deal with the jitter, you will never get there. These can beat your CD player by a long shot if you make the right choices.
Here are some useful tips (no advertising):
http://www.empiricalaudio.com/computer-audio/
Steve N.
Empirical Audio