Recorded SPDIF playback does not sound as good as original SPDIF input signal

I know when you record analog audio, the input monitor always sounds a little bit better than playback from the recording, because there is always some loss.

My problem, is that I'm recording SPDIF and I'm experiencing the same loss.

I am using Cubase SX3, using and M-AUDIO Fast Track Pro. I bought the Fast Track Pro in lieu of a more expensive unit because 99% of the time, I will be recording SPDIF, so I don't need anything fancier.

When I am performing, the SPDIF signal is going from the source, to the Fast Track, to Cubase SX3, back to the Fast Track, and to my monitors. It sounds really good. I am using only the standar EQ (the o for high frequencies) just a little bit. On playback, I also engage it because I guess when you record, it bypasses the EQ and record the un EQ'd signal. The EQ settings are Identical.

The source bit/sample rate is set to the same as Cubase, and the Fast Track handles those rates as well.

When I'm done tracking, the Playback does not sound as good as when I was playing. Some of the high frequency presence is missing and the recording sounds duller. I try to post EQ a little more to make up for the problems to no avail.

The source sound includes a lot of high gain fuzz distortion. The highs are extremely important to the overall presence of the sound. It's not like recording a standard sound; thick fuzz distortion seems to be a hell of a complex signal to track properly.

The reason I am recording SPDIF instead of analog is to circumvent the issue of sound quality loss during recording. In basic theory, a digital recording of a digital signal should be identical to the digital source shouldn't it?

If not, someone please enlighten me.

And if there is something about Cubase I am not understanding, whether it be a setting or some sort of degradation the software inherently does to the the sound, please help!

Thanks!