Exactly how do you have the 105 hooked up to your amp and how many speakers are you using? If you're using just the stereo outputs, you need to use the multichannel outputs, tell the Oppo your speaker configuration (2.1, 5.1, 7.1, etc.), make sure your speakers are set to small, and set an appropriate crossover frequency. You can also configure the stereo outputs in setup to be front left/right for the multichannel output so you can take advantage of the better outputs for your front left and right speakers.
The dedicated RCA stereo outputs are better than the L & R outputs of the multi-channel??? Why? Aren't they all being processed by the same DAC?
Yes ...same DAC but the circuitry between the DAC and outputs is different, NOT inferior to the 2CH but just different enough to produce a sound that Oppo describes as " ....delivering an incredible sound stage and an immersive surround experience" which they never said of the 95.
You should know that Oppo hired/worked with very well respected audio design consultants for the 103/105 series of products so don't feel you are being short changed if you are using the 7.1 or stereo outputs. They develeped a sound signature that fit the price points they targeted for the 103 and 105.