You cant send the LFE to the speakers, its a discrete mono channel that only goes to the sub. In a 5.1 system the entire frequency range is encoded in the 5 normal channels, and the LFE is encoded into the .1 channel. The LFE is 2 or 3 tp 120 hz, but is 10db hot of the normal channels. Without a sub, you still get this content but within the speakers channels and not at the elevated spl level.
If you want to improve the low end bass of the system, your going to need a sub, thats what they do. If you just want to increase the bass you have, you can used tone controls etc, but it will only stress your speakers more. Bass performance in that system would also be highly affected by the choice of speakers. No matter what you do, your system will sound devoid of bass if your only running little sats, but if you have large florr standers you will get a lot of bass from them. Just be careful with the volume controls with films as many have a lot of very low frequency content.