I'm not sure what the cryo-parts signal converter does, but if it's a DAC then you should be fine in that regard to at least get a signal, or does the Krell have an onboard DAC?
Either case, you'll need to go into the "Audio MIDI Setup" application and choose "Built In Output" under the "Properties for" pulldown menu (within the Audio Properties section of the MIDI setup app). Then select "Built in Output" and make sure it shows it's putting out a master stream if it's I-Tunes 8.0. I believe it reads "digital out" if it's I-tunes version 7.5. If the MAC is not sensing a device on the other end of the fiber optic line, it will not put out a SPDIF signal (again, the cryo-parts signal converter could be part of the problem).
Also make sure you have a fiberoptic "minijack" cable that works with Macs and make sure it's plugged in all the way. Other then that, it should work.
Either case, you'll need to go into the "Audio MIDI Setup" application and choose "Built In Output" under the "Properties for" pulldown menu (within the Audio Properties section of the MIDI setup app). Then select "Built in Output" and make sure it shows it's putting out a master stream if it's I-Tunes 8.0. I believe it reads "digital out" if it's I-tunes version 7.5. If the MAC is not sensing a device on the other end of the fiber optic line, it will not put out a SPDIF signal (again, the cryo-parts signal converter could be part of the problem).
Also make sure you have a fiberoptic "minijack" cable that works with Macs and make sure it's plugged in all the way. Other then that, it should work.