I upgraded the sub 6 to a klipsch rw-10d. It might be overkill
*googles*
Really? That tiny thing? If anything I think it's keeping you away from
a lot of content at meaningful SPLs! Just yesterday we were watching X-Men First Class at a good volume (the speech volume wasn't too loud, but it was about -3db on the receiver technically), and I was thinking this sub might be improved upon, in my room:
I wanted to make use of the sub 6 by using it in tandem with the rw-10d. I was told the only way to do that with the receiver I had is to use Three sub cables and a single female RCA to dual female RCA adapter to split the signal.
It's not the only way. It's the simplest, though.
Then I was told by a different friend that all this would do is either overload my receiver or kill the sub 6.
Line level outputs like a sub out operate at very low current. The only issue I see happening is your receiver being unable to drive a really powerful amplifier to full power.
He suggested I should just sell off the 2 klipsch subs and buy something paradigm (the guy I got this info from thought paradigm was way better then klipsch)
I too think you should sell both Klipsch subs

, but paradigm will barely be an upgrade. There's some
real upgrades to be had. You gotta be willing to spend money, give up floor space, and lose your perceptions on what bass is supposed to sound like, though. And you really need to go with an internet direct subwoofer company!
And if I go with the something new, should I up and go with paradigm or is my friend just overly bias?
I would not get Paradigm.
It's now your turn to blow your friend away, with two of these:
http://www.rythmikaudio.com/FV15.html
That said, before that I would personally be looking to get superior mains, before bothering with subs.