I think the Oppo and other similar players are more about build quality and prestige, and perhaps spin a disk a little quieter. If you are using HDMI, then bits are bits, as long as they are delivered to the decoder (typically in the AVR).
If you want to use the 105 for its analog output, then you might get an improvement in audio. If you want to use it with HDMI connection, then you are probably wasting $.
The Oppo may outperform some of the lower end players on the test bench, where they are feeding it the most brutal video signals, but real-world material won't show the difference.
Also, the Oppo customer support is the best in the biz. Good luck getting any customer support out of Sony
I would absolutely love to have a 105. But, all things considered, I have put less money in other products that do the job very well.
Concerning the optical connection, it will be great for 2 channel music. You will only get improvement going to HDMI if you want surround sound (optical can't do 5.1)