I just finished putting together the AB528 and mic input works fine and seems to be doing what it supposed to. The only problem I have run into is that the DI doesn't seem to work. I can turn it up  full and hear white noise but, no other signal than that. I also don't hear the relay switch click when I insert cable. All of the connector connections on the DI board check out. Any suggestions or troubleshooting I could do? 
Thanks in advance!