Fly has it right.
The best suggestion is to use the channel masters as the send level and keep it there don't mess with it when you find the sweet spot(til' it's driving the eclipse, with a little headroom for good measure)…..then use if you have one the effects return as your overall volume control which is basically a power amp volume control.
series the loop and external mixer is the best option(like a switchblade, or a suhr mini mix for great sound for a great price)
The amp will sound better with the channel masters cranked like that. It does on my head anyway. I use a suhr head(pt100) and switchblade with the eclipse(balanced) ran exactly like this.
