Ripping to a Mac, any software?

Heymikey, so you've got some top-notch gear there all-around.
I don't know, but it's fun guessing, and my first guess might be ...
I wonder if you might be losing anything in the Mac-to-DAC
USB to SPDIF converter. Just a guess,
my experience has only been with USB all the way:
Mac to Bel Canto DAC3 USB port.

I don't think the hard drive makes a bit of difference,
as long as it's not junk, and noisy -- in the same way one USB cable
is just like another, save maybe better fitting ends.
It's all bits in both cases.

There is a less known feature of the Mac that may potentially degrade sound quality. The Mac has an internal sample rate converter. I don't know if it is implemented in hardware or software but believe me, you don't want to use it in either case. The problem is that it is automatically engaged if the sample rate of the source material is different from the setting of the audio output device. For example, if you are playing a 16/44.1k track from iTunes and the Mac's audio output device is set to 24/96k, it will up-sample your track and output 24/96k signal to your external DAC.

The only way to disengage it is to make sure the sample rate of the source material is the same as the sample rate setting of the audio output device. To check that, you need to use the Audio MIDI Setup program which is usually located in the Application/Utilities folder.

Once you open the Audio MIDI Setup, click the Audio Devices tag at the top and look into the "Properties For:" drop down box. As soon as your USB to SPDIF converter is connected, it should show up as one of the selection. Now select that and look over to the lower right corner and you should see some controls show up in the Audio Output section. Now you can change the sample rate to match.

Sidssp, that's good info, some people are not aware of the Midi utility. I'm familiar with the midi settings, but due to my downstream hardware it is not possible to set it for a 16 bit rate, mine is 24 bit only. So I have mine set at 24 bit, 44.1 khz, even though the iTunes audio is imported at 16 bit, 44.1 kHz. It does not appear to be possible to set iTunes to import audio at a 24 bit rate from a cd source, please correct me if I am wrong.

Heymikey,
You are correct. iTunes does not convert sampling rate when dealing with lossless formats.

If you want all your tracks to be 24-bit, you will have to convert them with other tool before importing into iTunes.

Just curious, what downstream hardware do you have that requires 24-bit data?

Sidssp, I'm using an Empirical Audio Freeway 2 USB to SPDIF converter, then out to an Accustic Arts Dac1 MK3. With this configuration, there is no 16 bit rate option available in the iMac's Midi settings, 24 bit only. I do have sampling rate options if 44100.0, 48000.0, 88200.0 and 96000.0 hz, I leave it at 44100.0. The Midi options will change if I put in a different dac. I don't know if it would be worth the trouble of converting audio files to a 24 bit rate before importing to iTunes, I guess I could try it and see if it makes any difference. See quote below, from bigfishaudio.com:
"What is the difference between 16 and 24 bit?
16 and 24-bit refers to the sample resolution of the included samples. 16-bit is the standard resolution of audio CD's, while 24-bit is an enhanced resolution supported by many samplers. Some Big Fish Audio libraries are produced in 24-bit, while others are in 16-bit.
It is not necessary to convert from 16-bit to 24-bit. All samplers that read 24-bit files can also read 16-bit files, and while it is technically possible to convert 16-bit files to 24-bit files, there is no increase in fidelity and therefore no advantage gained by converting in this direction."