DAC/Pre-Amp Upgrade, R2R or Delta Sigma?

I am looking for a DAC/Pre-Amp upgrade. I have owned a Naim V1 DAC and I am currently playing from a NUC with a North Star Fluxio DAC. The Naim V1 was very upfront, lots of prat but not very well organised. The North Star was a clear upgrade. Also a Burr Brown DAC, but with a very 3 dimensional sound with lots of detail and zero listening fatigue. 

Sonnet Morpheus is on my current short list (R2R), and also Linn Selekt . What is the global difference in sound signature of R2R vs Delta Sigma? Suggestions appreciated! 
think you should consider the Denafrips line of R2R DACs. Some of the best I have heard until you get to the 5 figure price range.

I would look at an FPGA DAC like the Chord Hugo TT2 or a DAVE.  My personal preference and would say they are better than anything I have heard other than Esoteric or dCS stacks.  I became a Chord dealer I like them so much.  
Global difference in sound signature, not sure what that means. As long as a DAC's noise and distortion is somewhere around - 120 there isn't going to be much of a noticable difference. The thing is R2R DACs  tend to not measure well so some will roll off the highs and produce noticable distortion which I imagine is where their " sound signature " would come in. There are of course lousy implemented Delta Sigma DACs too but a well implemented one like a Benchmark DAC3 doesn't really have a sound signature it's considered very neutral so what' goes in is what comes out. Good recordings sound good bad ones bad. Try to narrow down to a couple and get a friend to switch them back and forth and pick the one that sounds better to you using only your ears not your eyes. 
Good recommendations. Chord and Denafrips. Some people say R2R sounds more natural, musical with better transient response, and Delta Sigma more precise, spatial with less distortion.

Good tip, using your ears and not your eyes. I thought this was Audiogon, or is this the AVS forum? Or even worse ASR. Nevermind.
I probably should have just said using my ears instead of my eyes have saved me a few $$$ and at least to me DACs have gotten to the point it's really hard to tell them apart unless they're really bad or try to sound different with tubes or something.