Help - Does my Virus Need a DI Box to take care of noise?

[circlingkailas]

Hi - Greatly appreciate any advice/solutions here. The core system of my home studio is:
Mac G5 PowerPC dual-processor running Cubase 4.5
RME Audio Fireface 800 connected to the Mac via Firewire 800
Hafler Amp
Hafler M5 Reference Monitors

Anyway, I spent quite some time getting this setup quiet, isolating power cables from audio cables and the result is a very quiet setup with no obvious ground loop problems. For example, for all my instruments, for example my Oasys, I can connect the outs directly to the Fireface and have no residual noise, buzzing, clicking, etc.

However....I have this problem with my Virus TI Desktop. When I connect either the SPDIF out or the analog outs to my Fireface, I get a noticeable low-level digital-sounding noise. Not a hum, not popping, but a fuzz that is noticeable component of each instance of sound output.

What can I do about this - is this simply a need for a DI box (although aren't the outputs of the Virus balanced?) or is there something else I need to consider? And what about cleaning up the SPDIF signal?

This is actually pretty frustrating considering that I have repositioned the Virus all over the studio to try to get rid of this noise.

Thanks to anyone who may have some constructive suggestions!

CirclingKailas