I agree with multiple subs for the remaining five channels and a few more for the LFE.1 channel.
The LFE.1 channel like the other discrete and independent channels should be allowed to play on its own. In my home cinema I run two subs, a 12ââ'¬Â Eltax A-12 R that caters for left centre right and surrounds to extend the lower frequencies with a bit more support. While a larger 18ââ'¬Â JBL professional DIY made JBL 4645 severs the LFE.1.
Its hard to tell sometimes if the LFE.1 is active, if the levels have been set right, its hard to tell, unless you playback a specific sequence and mute the LFE.1 and the extra low end support, which could be when Selene is punched in the face by Viktor the hard hitting punch is more on the LFE.1 at this point.
Other sub bass impacts remain on the other channels. It's a combination of going here or there its unpredictable you never know when the LFE.1 is going to produce some exclusive low end.
Getting phase and polarity correct can be easy with a Behringer DCX2496 controlling the sound system, I use one for the fronts LCR but need two more for surrounds SL SB SR and third for sub bass and LFE.1.
Looking at the little modes on an RTA where a sound pressure metre would make it rather difficult to see the small changes.
I also have a FBQ2496 which is acting as parametric EQ for sub bass and LFE.1 this can help a multitude of small problems, with quick and impressive results.