I am streaming .wav files from an iMac to 3 airport express.
I am current using the optical connection of the AE to connect it to my Denon AVP-A1HD and an analog connect to connect it to the Denon CX1 of the bedroom. Optical does sound clearly better than the analog connection (even when comparing on the AVP-A1HD), but the Apple DAC is very decent considering the price of the device. I'll also try using the wifi of the Denon, but have not yet had time to configure it.
Whether it makes sense or not to use the AE in analog mode really depends on the quality of the other components in your system, starting with the DAC (standalone of as part of your pre-amp).
It also depends on how you intend to use the AE. I tend to use my Esoteric SACD player when I really want to listen to music in an audiophile fasion. I use the AE more for parties or social events where it is convenient to have a few playlists you can just launch and forget about. It is also great to let the guests select themselves the music they want to hear using the interface of the Mac. In such occasion convenience is more important that the last bits of quality. If you are the same, then the difference between digital and analog connect will not be that relevant I believe.
I assume that you know this, but the quality of the digital files you will play will of course also impact. Go for a lossless format (.wav, flac or Apple lossless) if quality is important for you. You should also not forget to address the backuping of your digital storage system (a HD I guess).
I have also been using the Apple remote using an iPod touch and it does the job, very convenient!
One obvious downside of the whole thing though is that it doesn't have a wake up function as far as I know. This means that you need to keep you Mac the whole night if you want to listen to music from another room in the morning for instance. The Sonos is probably the same, but it is designed to withstand this, while an iMac probably isn't. Nobody wil even check, but I would be
very interested in knowing how this will impact the life span of the Mac, and therefore help with Apple sales in the long run...
Cheers,
Bernard