How to find the good CD recordings?

George, As far as a guide to cds goes, I don’t think Deep Blues will help much.

I see that All Music is still doing a print version Guide to the Blues (as recently as 2003 anyway):
https://www.amazon.com/All-Music-Guide-Blues-Definitive/dp/0879307366/ref=sr_1_1?s=books&ie=UTF8&qid=1533003716&sr=1-1&keywords=all+music+guide+to+blues&dpID=51rwbkoUEPL&preST=_SX218_BO1,204,203,200_QL40_&dpSrc=srch

I don’t think that they will get into the sound quality of different releases much, but it will probably help you identify albums to research sound quality for. As others have said, the Steve Hoffman Music Forums are probably the place most devoted to sound quality. It could take some work to find blues discussions there, but there are some. You can sometimes get sound quality info from Amazon reviews too.

A quick recommendation: Robert Johnson The Complete Recordings (The Centennial Collection)
The one with the brown booklet and j card, not the black one.

No, Deep Blues is more of a guide to who's who and what their history is. Not a buying guide. 

I had a Robert Johnson collection on vinyl years ago. Will look into the CD you mentioned above. I do not have a collection of blues music. Mostly just scattered singles from iTunes or southern music CD compilations (Oxford American some of which are quite good). I need to put together a collection of the basics.

Next time I'm in Clarksdale, possibly this fall, but definitely in April for the blues festival, I will spend some time and money at Cat Head music. The owner Roger Stolle (nice guy) who runs the festival teams up with Jeff Konkel who runs Broke and Hungry Records to do some documentaries on delta and hill country blues as well as a video series called Moonshine and Mojo hands (worth a watch). Broke and Hungry Records records a lot of the local musicians in an economically as possible way. I'll let Roger spend my money in his shop.

@n80,
For the Node, you plug your the ethernet cable to the Node into the router.  Then your RCA out from the Node into the preamp. Both cables are included. I think I use AV the port, but that part is not important you just need an open channel.  The Node initially will do a firmware update and blink red to green for a few minutes (that's not in the instructions) After that, download the app for free to computer, tablet or phone or all.  Use the app to sign in to Tidal and you are done.

For direct to computer/phone to Preamp you need something like this:    https://www.audioquest.com/cables/analog-interconnects/bridges-falls-series/evergreen
If you want to get a cheap DAC they sell that Dragonfly and it is a MQA renderer and plugs into your USB port. (same cord to Pre)   I personally think the sound quality out of the Dragonfly Black is not worth the $100 bucks.  Half the time I just plug that evergreen into the headphone out and don't hear any difference.

I wanted to not use a computer for music anymore so that's why I got the Node2. I've had it four days, and it's easily the best source I've owned. Mainly because of the convenience.  The internal DAC is decent and sound quality is very good. I have read many review that discuss adding an external DAC from the Node, and you can easily.  The increase in sound quality can be had, but the results vary widely.

@shadorne 
Dude, we are on the same wavelength.  I just discovered the Nils Acoustic live about two weeks ago. Try Ray LaMontagne live.

Regarding finding the best Zep CD, it’s kind of a crapshoot.
I’m listening to LZ IV today and all 3 releases are different. The US (1987) has little detail and poor imaging; there is no separation between vocals and drums.
Germany (1987) is holographic. A wide and deep detailed image, and great separation with drums in the background with a clear bassline. It’s outstanding.
Germany Target release (1984) is transparent with good detail and a 3D image. Drums have space behind the vocals.
And sometimes there is no difference in SQ between a first issue and a later release.

With all the different CD releases I own, the best sound comes from a pressing with a low noise floor. The pressing plants may get the same master, but like pressing vinyl, each facility is different and the QC is different. Pressing a CD is a physical process where the playing side of a disk is actually pressed into a very accurate formation.

Another example, I have a very clean copy of LZ I, but it will never equal the SQ of the later albums due to the noise in the recording. The master tape was recorded over many times during the mixing session, the source reels had many hours rewinding/FF on the ATR’s. And due to the tape wear there is noise and even bleed through.

I’ve discovered that finding quality CDs is no different than looking for the best vinyl release. It takes some research and buying several copies.