Question about LFE port and 2 RCA ports on Sub.

yes

Just run the cord from the lfe/subwoofer out into which ever input you choose on the sub. Doesn't usually matter.

Agree, but the thumb of rule is that you use the LEFT innput, not that it matters on a sub anyway. If you use a Y-ledd/splitter to gain innput on both LEFT and RIGHt you can espect a 3db gain on the signal. But thats totaly useless sincemost subs has a level controll and most recivers has a level controll as well.

I'm doing this right now because the LFE jack on my sub doesn't work properly.

I'm running a sub cable from the AVR sub out to the left line level RCA jack on my sub.

If you are using bass management from the AVR, then be sure to turn the xover control on the back of your sub all the way up if you are connected to one of the RCA line level jacks so that you don't have two crossover frequencies 'doubling' on top of each other (the sub and the avr).