Oppo 83 transport and DAC

Any of the DACs you listed should work fine with the Oppo. Each will sound slightly different as they are all different designs. You might do some research in the archives on DACs as there are many threads on the subject. I use an Oppo 983H as a transport and it does a fine job, though I'm sure there are superior transports. If your DAC is one that addresses jitter, or if you put a dejitter device, like Empirical's Pacecar, between your Oppo and DAC, you should be cooking with gas. Of those you listed, I've only heard four. Of those my favorite is the Havana. The Cal Sigma is a bit long in the tooth. The Benchmark is a perennial darling, but I've never warmed up to it myself. It does claim to address jitter very effectively though, and I have heard it sounding better than I could get it to sound, at various shows. A few more for your short list: Bel Canto DAC3, April Music Stello, Red Wine Audio Isabellina, Modwright Transporter (also a wireless server). A good DAC would almost certainly improve on the Oppo analog output, which is reportedly just very good, but not as good as it gets (as is that on my 983H). You should probably establish a target budget and do your research from there. Plenty of good choices out there to choose from. Good luck.

Take a look at the Citypulse 7.2X ($469).I use this unit with a 981 and a Z-Systems RDP-1,with good results.

There is nothing wrong with the DACS in the OPPO. What lets it down is the Analog section. Get the Analog section modded by one of the modders out there and you will have a superb player. No need for an external DAC.