That is a very good question!
The modified Sonica and 205 are identical to my ears. Our mod is the same and the analog stage, DAC, etc., are the same. You just need to device if you want a Universal Player or a DAC.
As for the Marantz, it is different, but on the same level. The tube and circuit type are very different.
I think the Oppo mods have the best bass and are the most dynamic. The Marantz has phenomenal resolution and bass and is also very good.
It is so close, that I would say that it really comes down to a matter of personal preference. We have done more of the Oppo mods simply because the Oppos are more well known.
I will also ask my mod tech and see what he thinks as they all pass through his hands pre-post mod.