If I'm running analog out from the Oppo to my receiver and I add monoblock amplifiers for the three front channels, is there any reason I shouldn't just run the front signals from the Oppo directly to the amps and bypass the receiver altogether? I don't really want the receiver to do anything to those signals since they're already being decoded via the Oppo, right?
Does your AVR have pre-outs? If so, that would be the place to connect amps. Splitting channels - some to AVR and some direct to amps - might introduce timing or phase issues as well as level problems.