iTunes: dynamics, midrange gone 'til restarted

Has anyone else experienced this? Upon occasion,when I have shut down my Mac Mini, then restart, and restart my iTunes, I sometimes get playback where the dynamics are gone, and the mid range is non-existent by comparison to it's normal function. This is not a subtle change in sound, it's very pronounced.
So far my successful work around has been to simply restart the iTunes, and the problem resolves.......until I shut down my computer again. I'm not absolutely sure it happens with every shut down, but it may.
This caused a pronounced freak out after taking my system down, installing my new DACMagic, and not figuring out for awhile that my sound problem was the iTunes, rather than the much anticipated DACMagic!
Anyway, anyone else? And is there a way to make this problem go away?
Did you check the MIDI settings to see if they were set to what you wanted at the point you encountered this problem?
I haven't configured the MIDI settings in any way. I'm using the Mac's output as the front end for my 2 channel stereo system. It appeared that the only thing I might want to configure would be the audio output, and it's already set for 2 channel speakers (my system is two channels). I'm not really inputting anything into the Mac as a music source....I just use it's dvd drive for ripping. If I want to play a disc, I use my external dvd player into my pre-amp, etc.
What settings should I consider changing, in your opinion?
One thing I can do, I suppose, is record the currently employed default settings, then see if they're different when I re-encounter the problem.
Yeah, the exact same thing happens to me. And you're absolutely right, the difference isn't subtle at all.

I thought I was going nuts, until one of my very "non-audiophile" friends (she rolls her eyes constantly) noticed.

I've never noticed this happening until recently. I'm wondering if it is because of iTunes 8.

I'm streaming into an airport express though, and thought the problem lay with the AEx or my router. Guess not. The sound improves when I unplug/re-plug my airport express.

I know common wisdom was not to use the itunes volume control and leave it at max (change volume on preamp/amp) but I've never noticed a problem before doing it on itunes. Now it experiences an instant degradation of sonics as soon as I do it.

So your work-around is simply to re-start itunes? What happens if you don't shut down your Mac-mini or itunes but simply stop playing music for awhile?

Sorry I can't be more help. I tried posting a similar question on a computer audiophile forum, but no answers. If you figure something out, let me know. It's a really annoying problem.
Elf73, I have my Mini "hardwired" to the DAC with a USB cable, probably as you deduced. I wonder if reconnecting the Airport changes a setting or such in the iTunes program? If I restart the iTunes, everything is ok.
I probably should report this to Apple. I just wanted to make sure I wasn't the only one with the problem.
It'll give you a heart attack if you don't remember it in association with the installation of new hardware!
Yeah it is very disconcerting...

I have checked and my settings haven't changed. And for me, with streaming to the AEx, I don't think the AudioMidi settings even factor in.

For you since you have it hardwired, it may be a different story.

I have mine connected to from the AEx into a DAC through a toslink cable.

I'm almost positive, from your description, we're encountering the same problem. The sound completely recesses at some point.

Once you re-start itunes, does it remain stable. That is, the sound stays to your liking?

I've read something Benchmark put out about the sampling being done either through itunes or the operating system, something to do with "coreaudio", or SRC (Sample Rate Conversion), "truncated word-length". I didn't fully understand it at the time (I'll blame it on jet-lag)...

I couldn't find the article, but here is one that may help. At least, it'll help with your AudioMidi setup:

Found it:

I'll re-read it, and if you can make sense of it in practical terms.. let me know.
Not sure how practical it's been, but it's interesting reading.
My experience so far has been this: The MIDI Pref window will allow me to set the Properties for the Builtin (Audio) Output to 96hz 2-channel-24 bit (my rig is a 2 channel setup).
But when I try to configure the Properties for the Audio Output for the DACMagic (C-Media USB Headphones), the window is only allowing a sample rate of 48hz (or 44.1) 2-channel-16bit. 96hz 2-channel-24 bit is not offered as a choice.

The DACMagic hardware is only showing an incoming sample rate of 48hz, supplied via USB cable.

So far I haven't managed to trigger any bad behavior while manipulating these settings....I'm just a little puzzled why I'm not seeing a higher sampling rate. Is the sampling device dependent, file dependent, both?

Wondering if I've buggered the settings somehow....