Asynchronous USB vs. SPDIF with regard to DAC upgrade

Makes sense @audphile1 .  But, I have direct experience with MM Tambaqui first using its internal Roon Bridge and then with the Auralic Aries G2.1 and 2.2. and Grimm MU1

The sound was more lifelike and palpable with the streamer.  The G2.1 was annoyingly unstable, the 2.2 rock solid.  But the Grimm upsamples everything to 192 and sounds great using AES.  Better than no upsampling and USB to my Tambaqui.  So the Grimm MU1 and the Tambaqui  are a great combo, using AES, and it just shows how equipment can be so specific.

First off, I think you'd be hard pressed to find any decent audiophile-oriented DAC out there where the USB input is not asynchronous these days. Anything older than maybe 2012-2014, then you'd have to double check the design specs, but almost everything beyond that will be async. 

Second, like many other things in this world, there's no single correct answer as to what is better. Async is not a magic bullet although it was a big improvement over the old methods in a variety of ways. Still, I have tried a number of great DACs that sound best from USB and others where USB is my least favorite. Sometimes AES is your best bet, sometimes I2S (but watch out for compatibility issues, there are many standards), and sometimes even plain old coaxial SPDIF. It really comes down to trial and error. 

@fastfreight yep. Highly dependent on the network cards implementation. As well as the streamer you’re comparing it to. Grimm MU1 is supposed to be a really amazing streamer/Roon core. 

Meitner EMM Labs, Playback Designs and dCS use Converse Digital streaming cards. They’re top notch. 
Bricasti uses some other network card…not sure what it is. 
When I had Lumin U1 Mini and Bricasti M3 I couldn’t tell the difference between using Lumin and built in M3 network card. Aurender N200 destroyed the M3 network card in sound quality. The difference was exactly what you described - the sound was more alive, more articulate and engaging. 
With Meitner MA3i I found the in-built streamer to sound livelier that the N200. But just as refined. It was a bitter sweet moment selling the Aurender as I really liked it. But I didn’t see any value in keeping it as it would be collecting dust. 
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My Innuos Statement has separate OCXO clocks for its USB and Ethernet outputs, and the USB is supposed to be very good.  I prefer the Ethernet output.

My Lampizator Goldengate3 has the JL Sounds USB upgrade card, I prefer the S/PDIF input.

I can run straight USB from Statement to GG3 with a FTA Sinope cable, Ethernet from the Statement to GG3 USB or USB from the Statement to GG3 S/PDIF.  I always prefer eliminating the USB output and or input. I do have USB in the chain, Sonore Signature SE Deluxe to Antipodes S20 but the net effect is beneficial.

I understand there are now USB outputs and inputs that sound better than S/PDIF AES/ABU but they are in very high end devices, or I have chosen my gear poorly.

Quality of a USB cable is very important. If you’re doing any comparison, use same level cables.