Hey guys,
I'm new to the forums and I know the "Help me with a HT Stereo between $1000-$2000" is among the more popular thread topics, but I'll try to be specific to my needs.

I've been trapped with only HTIB's in the past and finally have the budget to upgrade. My current setup is
Onkyo's HT-790 with a new
Yamaha RX-V1800 receiver coming in the mail tomorrow. My room is about 14'Wx18'Lx8'H and the layout I've linked
here. (Sorry for my poor drawing abilities.)
I would estimate I use my system 90% for movies and games and only 10% for music.
My question is this: For $1500, would I be better off just upgrading the Subwoofer and Front Loudspeakers (PB12-NSD with Axiom's M60 v2) and upgrade the rest in a year or two, or should I just get a full 5.1 set now like the SBS-01 with PB12-NSD?
Any suggestions would be greatly appreciated, especially if you think the front and sub upgrade is the way to go.
If I got a 5.1 setup, I'd probably use the RX-V1800's multi-zone feature and set the other two speakers in another room.
Thanks in advance for the input,
-Josh