The sub channel route, is simpler, but more costly...it's pre amp.
I don't need a powered sub with the towers...12" subs are part of the package, and the amp drives hard enough...not Harman-Kardon hard, but also not H-K price
(As tested with a set of Cerwin-Vega's at my buddies house...wanted to make sure this receiver had some balls when I got it, they don't quit let you test receivers properly at the mall)
I'd sooner spend the money on GOOD 8 ohm subs for the towers, like the 12" Cerwin's, since I don't have anywhere to put a powered stand alone anyway.
Sigh, but that takes me back to money I'm trying not to spend in the first place.