What type of AVR or AVP unit do you have, name and model and does it have a db display on the unit and what level do you usually set it to when playing a film back?
I’ll start with mine it’s a Kenwood KRF-X9050D THX select
Fader level is usually set to 0db.
In regards to fader level VS SPL db level when using pink noise is used to verify SPL db level at the sweet spot with all other channels set to equal SPL of 75db.
The set-up in my home cinema does away with the use of the internal amplification that is built into the Kenwood KRF-X9050D THX select, where I use the RCA phone outputs to give me more control and flexibility with additional graphic equalizers and audio limiters that are used to great affect. Yet the level is still set to 75dbc wideband pink noise.
The loudspeakers are all JBL from an array of matching JBL Control 5 for the (three-screen) to an array of x8 JBL Control 1 for the surrounds a few height surround loudspeakers that are not JBL but soon to be replaced with JBL Control 1.
Sub bass comes in an array of two different types one is an Eltax A 12-A which is used for the sub bass extension for the screen channels and surrounds.
LFE.1 is used exclusively via a professional JBL 4645 with a more tighter JBL 2240H sub bass driver and with a just one port blocked up, it delivers a slightly lower end when I tested it with a series of sine waves between 20Hz and 80Hz.