Just last week I installed an Airport Extreme and an Airport Express into my system.
The cool thing about the extreme is that I can dock via usb my seagate hardrive with my music back-up straight into the extreme. The extreme then sends the data wirelessly to my laptop running itunes and foobar (which is now functionally a remote control). The only hardship I experienced doing this was that I had to remap all of my songs to the now "remote" hard drive (about 180 gigs/30,000 songs). This took about a day and a half. Overall it is very fast, perhaps a touch slower than actually being direct wired via usb.
Previously I ran usb from the hardrive to my laptop and then via usb to a toslink converter ($30) into a Monarchy dip 24/96 and from the dip into a modified Tact 2.2x. As an aside I really feel that the Monarchy helps to clean/smooth things up quite a bit.
Anyway onto the express. Once I got the harddrive remapping sorted out, it enabled me to do a side by side comparisons of the express vs. the usb adapter with a simple toslink swap at the dip. I spent about a day or so doing this because in all truth it was very difficult to tell the difference at first. I would go back and forth maybe 20 times on the same passage of the same song to make sure that my ear/brain wasn't playing tricks on me.
At the end of the day the differences that I noticed were very subtle. 1. I found that the direct connection offered a "slightly" lower noise floor than the airport. This offered slightly darker blacks, and a sense of a slightly deeper stage. Low level details were a bit more layered and less forward. 2. The airport felt very detailed but perhaps added a bit more edge to certain sounds like symbols, which had a bit more etch to them and not quite as laid back sounding as they were with the usb.
Again, these differences were very minor but I ultimately felt that the direct wire was a touch more cohesive and easier to listen to. My final decision was to leave the express in but for critical listening go the direct route, when guest are over, or I don't want any cabling connected to my laptop, I switch to the express.
I hope this helped!
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