I've tried everything you mention EXCEPT the headphones, and that is an excellent idea. Will try it later this week when work lets up. I think my room is just too small for these subs. I wanted end-game subs because they'll soon move to a new, acoustically treated listening room. But the room they currently occupy is only about 11 feet wide and 17 feet long with 10 feet ceilings. Not a lot of room for 4 active and 4 passive subs. They still sound amazing, but I was expecting a little more and I've had issues before with connecting subs to the PrimaLuna (using line level and sub outs). Thank you for your helpful response!
PrimaLuna EVO 300
Any PrimaLuna EVO 300 owners out there experience very low bass? The voltage on the sub outs is so low that no sub would do anything unless maxed out. I'm now using stereo REL 212s, running line level, and that's provided adequate bass at about 60% gain. But I'm still surprised by how attenuated the deep lows are with my EVO 300. (By the way, I'm also using Cornwall IV loudspeakers, an Aurender A15 for digital, and Rega P6/Hana SL MC turntable/cart).