airport express questions


The airport express is equipped with a mini-jack that is a combo: analog and digital toslink. Monster sells a variety pack of cables to go with the unit, including a mini-to-full toslink cable, and a mini-to-RCA cable.
How can I be sure that I am streaming digital audio with airtunes? Is there a box in some dialogue window that I need to check? For analog audio, which I don't want, does the airport express have a crappy internal DAC, or would the laptop be wirelessly streaming analog from its own crappy internal DAC? Laptop is a 5 year old Sony Vaio, windows XP. Thanks.
realremo
Now, can someone tell me why, when running my airport express to a CA 840c using optical, that I periodically have an awful, glassy, fingernail-on-chalkboard sound?
Files are either alac or mp3 and with or without error correction when put on the confuser.
It doesn't happen at the same spot each time, but seemingly randomly.

Any suggestions?
Rbstehno - I rip files into ALAC not only to save space but also to avoid additional operation (ALAC compression) that computer has to do in real time to send data to AE (it is not a dedicated server).
the computer can do this and much more if you have a decent machine. when you stream your music, how much cpu are you using? are you telling me that you are maxing out your cpu? the computer has to do quite a bit of work to get data off the disk, into it's memory buffers, and then package it up to send it over the network. all of this messaging of data happens in memory, after it is read from disk. if you system is using less than 80% of your cpu, it is not a big deal. now if you are saturating the cpu, now you need to offload some processing.
the computer can do this and much more if you have a decent machine. when you stream your music, how much cpu are you using? are you telling me that you are maxing out your cpu? the computer has to do quite a bit of work to get data off the disk, into it's memory buffers, and then package it up to send it over the network. all of this messaging of data happens in memory, after it is read from disk. if you system is using less than 80% of your cpu, it is not a big deal. now if you are saturating the cpu, now you need to offload some processing.

I don't believe streaming music, either from the native hard drive, nor from an optical drive, is very CPU nor memory intensive. My tower is a dual 2.7ghz processor. I can monitor CPU usage in real time on the Activity Monitor utility. Streaming files from itunes runs average around 4-6% capacity of the CPU with a few spikes now and then to 13% which are very brief. It take 87mb of real memory and around 1gb of virtual memory to stream music as well. Not even close to the machines capacities on any of those demands. I have three Squeezebox devices around the house and can stream music to all three, different tunes to each one, without a hiccup and still check email and surf the Internet. This is on a Mac. The Squeezebox interface does use the iTunes library, but NOT iTunes. It uses a web browser and indicates even less usage of the computers resources than iTunes demands. It is not a demanding task for a computer as far as I can tell. I'm comparing it to something like Photoshop, video or gaming software that is very graphics intensive. Someone correct me if I'm wrong.
jax2 - you are correct. that was point in my thread above. unless your computer is saturating the cpu, then it will have the capability to do a few more instructions to stream audio. i have 3 separate zones off my mac and it is barely doing any cpu or IO. what you will see normally is higher IO and not CPU. but again, nothing that a newer computer can't handle.