As others have said, it's not a tube vs r2r comparison, but rather tube vs. solid state and/or r2r vs delta-sigma.
My main amp is a Line Magnetic LM-218ia -- an 845-based integrated SET amp. I have two DACs: a Black Ice D-S Tube DAC (GlassFX Tube DAC DAC DSD Wifi) and an Audio GD r2r Solid State DAC (R2R-R1). They are both connected to the SET amp and both play through the same Omega Outlaw Super 3XRS speakers (with built in 8" subs).
*the Black Ice was modified by Radu Tarta with some nice upgrades.
I find both of these DACs to be excellent, and honestly they are more similar than they are different even though they are using different conversion techniques and utilizing different output stages. In neither case would I say one or the other was a bad match for my SET amp -- they are both excellent.
If pressed I would say that I prefer the Audio-GD. I think it's a bit more revealing and I find the imaging and separation between instruments to be slightly more defined. Both of these DACs are in the $900-$1200 range and I just think they are both a testament to the quality of sound that is attainable at a relatively accessible price (by audiophile standards where an interconnect can cost as much and does far less).
-Chris