hi PilerTyler,
it would appear that this email got lost in the shuffle around here so i will do my best to help you out. While i'm not perfectly familiar with all of these components we'll see if we can struggle through this. If you are adding a Onkyo 705 receiver that will change things a bit too.
Oppo to Onkyo - HDMI cable (single cable should carry audio/video on DVDs as well as audio on CDs/SACDs/DVD-As)
Monoprice HDMI Onkyo to Optoma - HDMI cable
Onkyo to speakers - regular speaker cable (depends on distance, but usually more than safe with 12 or 14 ga)
Onkyo to EP500 subwoofer - regular shielded coax cable with RCA ends
Monoprice RCA Note you don't need a fancy coax-RCA cable that is listed as a "subwoofer cable". Any cable with RCA connectors will do.
This is probably the cheapest and easiest way to hook things up. Of course if you are adding other components into the mix such as a VCR, satellite receiver, HD-DVD or BluRay, etc then it will increase your cabling needs. However, the nice thing is that with your Onkyo 705 you will still only require one cable to the projector and the receiver will do all the switching for you.
There are millions of options for where to buy your cables, but in general the best/cheapest bets are Monoprice for your HDMI and sub cable and a home improvement retailer such as Home Depot for your speaker wire (they usually have this in bulk). One other suggestion i love throwing out there for fellow Canadians is to check your local Princess Auto store. They often carry a large selection of audio/video cabling that is of comparable quality but at significant savings.
