I haven't heard the Wave Tube DAC but I own a Tubadour IV SE R2R DAC. This DAC is very good and has operated without issue. The buying process was great - it was nice dealing directly with the owner/designer of the business and everything went as planned. The rest of my comments will probably not be as satisfying but here goes.....
I have owned a bunch of DACs over the years and currently I have a Berkeley Reference Series II MQA, a Black ICE Glass FX Tube, and the Audio Mirror. I have usually run at least two DACs in my system so I could compare them over a longer time span. I have also have multiple CD and SACD players. After years of comparing one DAC with another (and one player to another) I have concluded that they all sound very, very close, if not identical. If you disconnect your old DAC and hook up your brand new $20,000 DAC I guarantee you will hear the angels sing. But if you have both DACs in your system and compare them against each other over a period of months I think you will come to the conclusion that there isn't a whole lotta difference. Double blind tests have shown again and again that even highly trained listeners can't tell one DAC from another.
I also have a Jay's CD3 MK III transport plus a Teac 701 T transport. They are both wonderful pieces of gear and I could live with either one. The reason I have both is because the Jay's dithers the 1st bit and so it won't let the Berkeley decode HDCDs. I have quite a few discs in this format so this is an important consideration. The Teac preserves Red Book format plus it also will read MQA discs and do the first unfold so the Berkeley can finish the job.
I could never be a professional reviewer because I approach this hobby from a scientific perspective where I always want to have a control for comparison. It's interesting that the DAC reviews in Stereophile and TAS are toning down their rhetoric on digital gear and tacitly admitting that the sonic differences are becoming smaller and smaller.
My advice for folks upgrading their system is to assume that modern digital gear is going to sound pretty similar and to buy components that give you the best pride of ownership that you can afford. If the story and the look&feel of an Audio Mirror flicks your bic then go for it and don't look back. If you are a person who prides themselves on getting the most for your money then there are fantastic Chinese DACs that are reasonably priced. As quality gets more compressed, I think that this hobby is shifting to a market where enthusiasts are buying gear on the story, the looks, the price, and peer opinions rather than on sound quality. This is fine because it is getting harder and harder to buy anything that actually sounds bad.

