I'm running the following equipment and have traced the problem to the Zbox.

CD Player to ZDAC to Zbox to SE84ZS

Running in this configuration I have to turn the volume completely up on the amp and put my head to my speaker to hear any sound (but there is CD music)..If I bypass the Zbox and run direct from the ZDAC to the amp everything works fine, normal volume.  Yesterday the entire setup worked flawlessly.  

I have tried two different tubes in the Zbox with the same low volume result, so I do not believe it is a tube issue.  I have also turned the gain knob with each tube and nothing different happened.  I also checked the fuse and it appears to be fine as well.

Anyone have any insight on what the problem may be?  

Thanks.