Sorry if this is somewhere else, couldnt find it exactly when I searched. Here is the question: Is there any benefit to splitting an LFE cable with a Y and plugging them into both the L and R inputs on the sub? Normally you would run a single cable from LFE to either L or R, I know. But my cable came with a FMM Y cord so I can run single from AVR then split it at the sub and plug signal into both L and R. thanks and sorry again if this is obvious and/or somewhere else. Thanks in advance.

It normally doesn't matter. Try it with and without the Y adapter and judge for yourself.
Normally the "left" input of the sub is for a "mono" connection. Check your sub's manual for specifics/recommendations.

I guess if your sub has a L/R input then use them if you have the connector......my PW has that but my previous sub (Servo15) just had the mono connection.

I'm thinking the difference is minimal, probably along the same lines as bi-wiring. ;)

Try it both ways, but generally in my experience there will be quite a bit more gain with a y-connector to both L/R inputs.