Re: New to the Obsession
First I would wire the speakers directly off the receiver, then the sub via the RCA jack (I am assuming it's a powered subwoofer, if it isn't, then you will need to keep it wired as you have it)
Do you have an SPL meter???? Device to measure sound pressure levels, they can be had @ Radio Shack for ~$40 (buy the cheaper analog one, not the digital one) and go through speaker setup and adjust the levels, likely your center channels levels are low, some speaker do not reproduce voices well, so this is also a potential problem. You might also benefit from placing the center as forward as possible on that shelf to aid with it's dispersion, this might also help some enhancing the vocals.
Your speakers also seem to be positioned a little off. The fronts are very close to the AV stand and look to be toed out, try moving them around, rarely do speakers sound best 'toed out', see what you can do and adjust the angle to see what sounds best to you, you might also play with varying the distance to the rear wall and watch for changes in bass response.
Your rears seem to be almost on the side of the couch and aiming forward, I would try them off the the sides and behind and aiming at the seating position, you will of course need to readjust the speaker distances and levels after finalizing what works best for you and your room.
As for the cable, you can get 5.1 from it, just wire a digital out from the cable box to a digital in on you HK receiver and you'll be set.
Good luck and keep us posted on your progress!
Ken Taraszka, MD