RM6900 (LFE & LineIn)

I'm a noob at this so I hope this question is not too dumb ... :)

I just bought the Polk RM6900 speakers and they are awesome. However the manual makes no mention of what the LFE and L/R Line-In options are for on the bass box.

Can anyone help me with this? I've got a great receiver (Pioneer VSX-1015TX) and I would hate to be losing out on some exra features that the LFE and Line-In might provide.

Thanks
Ian