Which way to go? Airport Express or USB interface

Read these two links:

http://www.positive-feedback.com/Issue22/nugent.htm

http://www.wavelengthaudio.com/usbdac.html

and tell me if you still want to go with an Airport Express. If it's convenience you want, go with the Airport Express. If you want hi-fi performance from your Mac G4, get a USB-coupled DAC from someone like Wavelength Audio, Apogee Electronics or Ack! Industries (when their new USB option for the Ack! Dack! comes out).

Some misinformation appears above...

the USB connect has the potential for better performance since the Airport will convert everything to Apple Loseless

Apple Lossless is exactly that - lossless. There would be ZERO performance gain or loss. Both 802.11g and USB 1.1 have enough bandwidth to stream cd-quality audio so this is not an option. If anything, the Airport Express has an 8-second buffer that USB does not so there's additional protection against network dropouts if you're streaming audio in from the net.

Indeed the USB route is limited to 16 bit (redbook CD).

Neither USB nor 802.11g is limited to 16-bit/44.1 KHz. Both can handle increased bitrates, should that ever become important. It has absolutely no relevance in today's world, as the high definition formats are completely encrypted all the way to the DAC. That means there'll be no digital streaming of SACD or DVD-Audio anywhere!

some of the best DAC's are designed (intentionally) for 16 bit

Actually, all of the home/hi-fi DAC's are designed primarily for 16-bit input (even the dCS). It's only in the pro world where you would need to handle 24-bit streams.

Coaxial methods being preferred by many as the better way to stream digital info

With jitter correction circuits you won't notice the difference. I've tested USB into an M-Audio Audiophile through a $100+ Chord Prodac vs. the Airport Express and the Monster Cable optical and can't tell the difference.

I'd suggest a USB DAC like the Benchmark

The Benchmark DAC-1 doesn't have a USB input, and when I asked them about this earlier in the year they had no plans of adding one. I'd bet their space in that case is too cramped to add any more boards.

The bottom line is that the quality of sound you get out is in direct relation to the quality of the DAC. Everything else in the middle is pretty much irrelevant except when it comes to convenience.

I have been using the AE and loving it. I use a optical connection to my DAC in my BK Reference 20 and am quite please with the sound quality.

Ghunter's post has some useful clarifications. Also, Airport Express does not "convert everything to Apple Lossless." iTunes converts everything to Apple Lossless, _if_ it is being used to wirelessly stream audio data to AEx. But this is kind of academic, since, as Ghunter says, AL has been shown to be a true lossless format.

"Coaxial methods being preferred by many as the better way to stream digital info"

With jitter correction circuits you won't notice the difference. The bottom line is that the quality of sound you get out is in direct relation to the quality of the DAC. Everything else in the middle is pretty much irrelevant except when it comes to convenience.

I think the wireless technology combo of AEx and Apple Lossless works great. The ergonomics/convenience of using iTunes and being wireless is terrific, so that's where my vote goes. I did become curious about whether the optical feed from my AEx to my DAC was a weak link. I ended up purchasing a Monarchy Audio Upsampler DIP, which of course goes way beyond just substituting a coax feed for the optical. The results are noticeable and worthwhile, even though I am using a good quality DAC (Northstar Model 192) that is supposed to have very good jitter reduction circuitry of its own. It makes sense to me that jitter reduction can be a cumulative endeavor, and I think if you are using a modest source (AEx, DVD player, midfi CDP, and I would imagine devices like Squeezebox and Waveterminal), lightening the jitter-reduction load for your DAC by using some kind of anti-jitter box before the DAC can be worthwhile, especially given how inexpensive some of these anti-jitter units are on the used market. However, I don't want to sound like one could not possibly be happy without making this extra investment. I was very pleased, very satisfied with the sound from my AEx running straight into my Northstar, before I added the DIP. It sounded great; I didn't find it deficient at all. I just got curious.

If you are using a Northstar DAC, you should try an Empirical Audio Off-Ramp I2S. This is a USB to I2S converter. Simplest way to get data and clock to the DAC chip. The RJ-45 connector should be compatible. Do you want to be the guinea pig?