great choice in players
it would be a great combination but honestly all blu-ray players & modern receivers do 5.1 which is the most basic & common surround setup in a living/family room environment. The Oppo happens to be a top rated, full featured robust player plus you can't go wrong with a SC-67 as your very 1st surround receiver coming from stereo. That would be a great setup that will take care of your surround audio needs.
actually with new receivers like the 67, if you decide to add more channels past 5.1, you can go as many as 9.1 (with 2 subs), which can include height & wide channels.
your understanding of 5.1 surround is correct but as clarification, what you call the "rears" (the 4th & 5th channels out of 5.1) are more accurately called surrounds or side surrounds to distinguish them from true rear or back channels. The preferred location for them is more to the sides, from 90 deg to ~120 deg from the main seating position to the sides but slightly rearwards. Rears or back surrounds are the 6th & 7th channels in a 7.1 setup. When you say "rears" most people will assume you mean those back channels.
now if you're really going to mount the surrounds directly behind you, you can, just as long as you remember to wire those speakers to the surround outputs not the rear (or back) outputs. this is important because in 7.1, most of the time, those back rear channels are derived from the side surrounds.
5.1 = fronts, center, surrounds (side surrounds)
7.1 = fronts, center, surrounds, rears (back channels)
9.1 = a) fronts, center, surrounds, rears, height channels or b) fronts, center, surrounds, rears, width channels
11.1 = all of the above with heights & widths at the same time
you can find excellent diagrams of various setups, recommended speaker locations & terminology on Dolby & DTS's websites - here's a couple of links that may help,
especially when you start adding matrix processing like Dolby ProLogic IIx (to get 7.1 from 5.1) IIz (adds heights) & DTS NeoX for the same things. Most Blu-rays & DVD's are natively 5.1 but some are encoded as 7.1 with dedicated rear channels. The majority of the time, we add ProLogic IIx or DTS Neo to get our 7.1 channels from 5.1.
Most receiver manuals, including Pioneer's, have speaker layout diagrams & descriptions of channels:
hope this helps as you move from stereo into surround sound Edited by ss9001 - 9/25/12 at 1:15pm