Does Apple airport express work well?

An Airport Express IS a wireless router, so depending on your layout, you may not need another one.

It's a fantastic music streamer, as is an Apple TV if you want visuals to go with your music, but Apple TV does need a router.

You can't connect the USB port on the Airport Express to the USB input on your DAC, optical is the only option. The USB port on the AE is configured for printer output only, there's no music signal available from it.

I can't get mine to work at all, so I've been using the analog outputs (bummer). I know it's just a setting, but for me (technophobe) I can't get it to work. Money wasted, sadly, in my experience.

the AE is a simple device that works either wired or wireless. i have mine hooked up both ways without any delays or dropouts. if you are getting delays wireless, try changing the channel. i had to do that a few years ago and haven't had any issues since. if you get an AE, get a newer unit with 'N' capability. also, get a good glass toslink cable with a $2 mini extender for use of the digital out. this is a much better than going the monster cable route with the extender built in.
i share a printer using the usb connection, can't use it for anything else.

i have been swapped out a couple of AE's for Apple TV's with better results. you can pickup a used 40GB apple tv for around $100 used, compared to $100 for a new AE. When using an AE, you need an extender for digital out. the Apple TV has a true toslink out along with rca for audio. i don't store any data on the internal drive but you can sync up your photos, videos, and your audio from your itunes source. your apple tv can be a front end to your music server. you have the option of communicating to the apple tv with its simple menu system and have the apple tv talk to the music server to stream. you could download songs/videos/photos to the apple tv and just access them from the apple tv instead of using the server. plus you can hack the apple tv to get many other feeds on it and to allow the connection of an external hard disk. this opens it up to hulu and many other sources.

another big benefit is flexibility using the apple tv. when using the AE, all destinations with AE's have to listen to the same source. using apple tv's, each room can listen to another song than the others off the 1 music server. i can listen to jimi hendrix in my audio room while my listens to celine dion in the bedroom, off the same music server. and you can do this without storing any data on the apple tv.

i never go directly from the AE or apple tv into the preamp. i always use a jitter device 1st, then go into an external dac, then into the preamp. if your preamp has a good dac built in, then still use a jitter device between the 2.

I have all that stuff. My DAC reads something because it locks on the frequency, but no sound.