Oppo 205 DAC

It really depends on the implementation. Some R-2R DACs can sound rolled off because they're non-oversampling and lack the reconstruction filter as well. These will naturally have a droop in the treble region.

Having said that, what really matters is the quality of the output overall and that's where measurements come in. Find competently designed DACs within your budget and try to audition those.

I own the 105 (in my two channel system) and when Oppo announced they were going to cease making players immediately bought a 203 for one of my HT Systems.  I regret not shelling out the extra few hundred back then for the 205.
  At any rate, I used the 105 for a while as my DAC, and then ultimately bought a Mytek Manhattan (first generation), which uses the exact same chip as the 105.  The Mytek blew the Oppo out of the water, which is no disservice to the Oppo, since the Mytek cost 4 times the price of the Oppo, and the Oppo has many non DAC related functions to perform, but it did illustrate to me that it isn’t just the chip that makes the DAC sing.

Everyone is going to have their opinion on what they prefer which is how it should be. I also own an Oppo 205 and frankly my RME DAC destroys it, but that’s to my ears and my system.

I’m not up on the Topping DACs, but isn’t the D30 their entry budget piece? If so I’m sure the OPPO does sound better, especially if you’re by chance going Toslink into the Topping. The 205 definitely sounds good on its own and if you don’t compare it to quality DACs, most would be more than happy with it. It’s also built like a tank and very flexible and for that reason I’m keeping mine regardless of what they’re going for these days. 

Isn’t it the Topping D90 that gets a lot of attention? Before you kick your D30 to the curb, what connection are you using for digital input? If Toslink go SPDIF coaxial and use a decent cable. Next are you using the power cable that came with? If so, get a better cable as that will likely help as well. Make sure to stay with a shielded power cable. These tweaks will help but maybe not get it up to the Oppo or I suspect the better D90.

It ain't the chip but how it's used.
All you have to do is listen. Ignore the rest.
Better off with no "chip."

I liked the oppo so much I pushed it further with a modright which helped with added gain but otherwise minimal improvement. Still love its sabre implementation.

Do R2R designs lose detail or have rolll off? 

I do have the same player and have been using the player exclusively as a DAC since July last year. I love the way it makes music and ever if I might get a dedicated DAC in the future, I might use this player for playing BluRays/DVDs in another system.I have a Auris BluMe that has the AKM DAC and while it is a Bluetooth receiver, it does sound pretty good. I don't think the "chips" sound so different. I think it might be the "implementation" that might be making the difference. Was hoping to get a DAC with AKM, but the factory is burned down. So R2R might be something I would be interested in. Honestly I am sick and tired of ESS Saber chips. Not that they sound bad. In fact they sound pretty good. But I see them everywhere - a little bit too much.