"....REL suggested first unplug yellow wire from speaker terminal and turn up sub gain as that might improve the bass integration...."
Do NOT leave the yellow wire floating! I recently traced a low-level rumbling sound to an open connection between the yellow wire and the Left Speaker input inside the Speakon connector.
Do NOT leave the yellow wire floating! I recently traced a low-level rumbling sound to an open connection between the yellow wire and the Left Speaker input inside the Speakon connector.