Responses from motokokusanagi

Digital cables Kimber d60 vs Nordost Valhalla digital cables
What transport and DAC are you using? @shkong78 is totally right; it’s all system dependent. However, when talking RCA spdif cables, my experience is there’s almost zero correlation between how you might like one brand’s analogue cables (or even o... 
Replacing Alpha Core Goertz MI-2 Veracity Speaker Cable
The best speaker cable I’ve ever owned was the old Townsend Isolda. These were based on your Goertz flat ribbons (zobels and such) but different insulation and cryo’d. Imaging was huge, treble was sweet, and the bass was un-be-lie-vable. Like addi... 
Aerial 5T impressions
There was an old comparison in Stereophile of the 5B to the SCM19 V1; kind of came out in a tie. I have the SCM20 pro passives (virtually same as the SCM19 V1). I love them, and find the low end remarkable for a sealed enclosure. It’s accurate and... 
ATC SCM40 in house tweeter & midrange
The faceplate/waveguide and number of screws. 3 on the new ATC tweeter. 4 on the old Seas one. All versions use the ATC mid. 
Any comments on AES/EBU XLR digital cable VS. BNC Cable
Although @lalitk's comments are wholly reasonable, the variability of quality of digital inputs is going to be DAC by DAC. Having established the N10 AES sounds better (as the master clock) than the Simaudio USB isn't the same thing as saying that... 
ATC users
I defer to tobes’ positive experiences above, however, the cost of 2 AHB2s + SCM19s is higher than a pair of fully active SCM19As and getting close to SCM40As, too, so wouldn’t think passive biamping is the ideal thing in comparison. 
Best return for the money, system upgrade suggestions please.
Unless your room is already done, 100% acoustic treatments! Check out GIK Acoustics stuff. No gear upgrade can match the sound per dollar spent on acoustics. Next would be speaker placement (free!) 
Bluesound vs SOtM
Wait up. The Codex can be used in preamp output mode with USB input; that’s one of its features. Check the manual You’re making the assumption that the brittle sound is due to t... 
Relaxed, musical DAC around 2k used?
Of used listings atm that I've heard, there's an M51 for a good price (I  still use one!) and the aforementioned Auralic Vega. Also a Metrum Onyx which might be up your alley. 
3 Options of Speakers + Integrated Amp. appreciate all the thoughts about..
No experience of them! But why these particular pairs (seems limiting)? 
NAD C 375BEE Integrated Amp Replacement Recommendations
There's a used NAD M3 listing atm. Heard this at a couple shows and sounds smooth and powerful. It's an older item, though. They just released a streaming M10, which might be worth a try and new, it's within your budget. 
Does this exist? Preamp/Streamer/DAC with MQA, Roon and more
There are only so many devices that meet your criteria; they all seem to be listed on the mqa website under the streamer section  HDMI would be the sticking point that might make you look at the mainstre... 
Need to under stand Asynchronous USB
...the Marantz is doing the playback; the iPad is just a remote control; your wifi network contains all the data being sent to and from the Tidal servers 
Auralic Aries Mini..... How much? wow
Clueless pricing. I think it's actually more than it was new several years ago! 
Need to under stand Asynchronous USB
It depends on the device. The old squeezebox touch's digital out was better wired vs wifi, but times have moved on, e.g. with the new Auralic stuff, wifi is reported to be equal if not preferred. You can just try comparing the two on your Marantz.