In the interest of saving cash, and I have the wire) I was going to run rg6u across my ceiling and in wall to run my base channel to the new but kickers basically I would have the receiver y off of the RCA to the fantum 113 then the other y to the wall jack via a sub cable then to rg6u across the room about 50' then to another wall jack and another sub cable to the butkicker amp.

I don't want to degrade my base signal in any way and am always cautious about splitting it. Especially given the level of equipment I have.

Or would one good sub cable from blue jeans be better than all the wall jacks?

Splitting the output will have minimal affect on the signal strength.

On a 50 foot run you may want to use a shielded RG6 cable. You can try straight RG6 and see if you get any RF interference in the form of a hum.