Responses from hau72

Rel sub cable options
Signal Cable does not state what kind of solder it uses. I am wondering if it just regular and not pure silver solder as with the Rel Bassline Blue. 
GaN Amp & Speaker Popping Sound At Power On
Yes, in Pro Audio, you do turn on/off equipment in a specific order to avoid pop noise.  However, this particular GaN400 makes pop noise with only the power cord and speaker cables connected to it and nothing else. 
GaN Amp & Speaker Popping Sound At Power On
I just received my GaN400.  Mine has the same popping noise on power up as you described.  I emailed the salesperson and explained the problem.  She said the pop/static noise during startup is normal for this amp, it will cause no harm to the amp ...