There is a left and right bass signal. Period. If you don't use the LFE you won't get the full signal by using only one RCA. That is the same thing a LOT of people can't seem to understand. The signal is NOT MONO the results is MONO in nature because it's omni present below 60-80hz. The Complete signal from the source usually has even more than just a left, and right track they can have a signal that is surmised (3rd channel not TRACK) also. Guys that play BASS will chime in and tell you they don't record MONO bass tracks for playback.
DBA misinformation is the problem.. Just because is sounds better doesn't mean it's playing the whole bass track especially if only the left or right signal was used.
Yes if the signal being sent to the plate amps is through junk RCAs that can cause a signal loss too and you will have to crank it to get any bass out of it or increase the signal. Either way more is better.
Better BASS resulted from a better signal to the sub plate amps.
Another thing LFE bass is modified. It has a step baffle to increase the signal, that is what you experienced. not all LFE signals are the same and some can be modified vs onboard options..