Not sure if I completely agree with you, Matt. The Oppo is pretty much a "swiss army knife" of players. It is a universal player that will play pretty much any media (audio, video, bluray, etc.) with an excellent video processor and a very good analog stage with analog outputs for both 2-channel and 8-channels audio. For the money, you cannot beat what the Oppo provides for you. However, there are definitely going to be better DACs or players out there.
The Marantz is most likely going to sound much more musical in comparison. With the Marantz, you a looking at a player that is almost twice as much, but is only focused on being 2-channel player/DAC (no video and no multi-channel). You'll have better internal components as well as less hash from video/DSP stuff. I have read other posts where a person had an Oppo but chose a Marantz bluray player because the analog output was warmer and more musical.
It depends on what you want. The Oppo 105/205 will sound very nice if you put it through a good preamp.