It is confusing because the LFE connections on the towers might seem kinda' redundant and the center channel is mislabelled. These front and center channel speakers are specified by Def Tech to be set at Large(Full Band.) The LFE port on the center channel is actually meant for the center pre out of a processor or receiver. Though, I would like to torture one of those center channels with an LFE connection. If using option 2 for connection of the towers, which is using the LFE cable connection as well as the speaker wire connection, the receiver's Subwoofer setting needs to be set at YES and Double Bass does need to be ON since the front are set at Large(Full Band) or no signal would be sent to the LFE channel pre out for output.
Here is the issue with these speakers regarding bass, Dolby Atmos and DTS:X. Combining the powered woofers in the same box with mids and highs means compromising low bass since the optimal layout for a front stage may not, and is often not, the optimal place for subs and these aren't exactly subs. The other issue with the front speakers and the surrounds is that they were designed for channel based systems and Dolby Atmos and DTS:X are object based formats that don't work optimally with bipolar type speakers. Upfiring Atmos modules placed on front speakers are also problematic as the sweet spot may not coincide with the front speakers' sweet spot and both may be compromised.
So, try setting the center at Large(Full Band) and turn off that f#%kin' Dolby loudness management feature in the receiver as it is ON by default. Many will recommend the purchase of a capable subwoofer or two for your system for proper bass output and they are not wrong. You may never get a good "punch" without one or two of them. Leave the LFE connections as they are in the front speakers for now. If and when you get a sub or two, you will simply transfer the connection of the LFE cables from the fronts to the subs. It's at this point you want to set all speakers to SMALL and run DIRAC. I don't think an external amp is really necessary here. Whatever you do, have fun with it.