LFE vs Line In

[Dubious]

I recently gutted and modernized a Yamaha NS-W2 for my father. I replaced the stock 40w amp with a 150w plate amp and replaced the stock 10" driver with a Vega to give it some oomph.

The sub works great using high and low-level inputs, spitting out tremendous SPL. However, when I connect my receiver's LFE output to the Left Line In on the sub, the volume level is extremely low. When I connect my normal HT sub (Hsu VTF) it has great output so I know that the LFE out on my receiver is functioning properly.

I tried reading up on the specs for LFE vs Line-In signal strength but was unable to find anything useful.

Since the plate amp that I installed does not have a dedicated LFE-in port I assumed that connecting the LFE channel to the Line-In would give the same results. Am I incorrect? Is there a fundamental signal difference between an LFE channel and a Line-Out?