Ok, the first issue I’d have with your setup scenario is that the rears would go unused when running a 5.1 movie soundtrack. The Oppo doesn’t feature any processing to steer some of the sound to the rears.
While your room may have great acoustic treatment, as you know you’ll probably need some Eq to smooth the room response even more which the ARC will do for you. And if the processor is Audyssey Pro capable, you could have a pro tweak it even further.
If you’re dead set on sending the video signal straight to the PJ, which really isn’t necessary given the level of processors we’re talking here send the signal through untouched, you may want to consider upgrading your Oppo to the 93/95 model that has the dual HDMI outs.
And if you’re against an unbalanced to balanced connection then only a pre-pro will do so I’d suggest the Marantz AV7005.