I tried yesterday evening the Y-adaptator (don't have XLR-Rca yet) and was surprised that I need to turn the volume at is maximum to match my horns (99db efficiency, so it is normally close to the Prometheus). Then I put a "burn-in CD" on my Cd-player and noticed that one of the woofers was moving much more than the other (same phase, crossover and volume adjustement). So I have to check all my set up (wires, connections, etc.) and to try poweramp connection too. Will wait until the burn in of the woofers to post a commentary on the results.
Thank you again, DIY is fun !
J.-F.