I don't understand the question.
Optical cables are cheap, yes. You can connect your Oppo DVD player to your Denon 2805 via an optical audio or digital coaxial audio cable. Both transmit the same signal. You need one or the other to get Dolby Digital/DTS.
So, if you're not using a digital audio connection from your Oppo DVD player to your Denon receiver, pick up an inexpensive optical cable.
I'd recommend
www.monoprice.com though. Quality on eBay can be inconsistent at best. Monoprice is every bit as cheap and their quality is high across the board. $3.27 for a 6 foot optical audio cable with a very thick, flexible cord, for instance. Their shipping is very inexpensive (probably $2 - $3 for the cable).
