If I don't specifically have anything routed to LFE, low frequencies from the regular soundtrack below a certain range will still feed to the sub, right?
I think that depends on how the receiver is set to decode the material. If you're playing back in discreet 5.1 and don't have anything going to the sub, you won't have anything coming out of the sub. If you play back on a DD2.0 system it will attemt to make it 5.1 and send some signal to the sub....I think.