@kgp - there is a pretty cool utility called Speedy Net on the App Store (I think?) that is pretty reasonable in cost. And from the command line, there is always iperf. You seem like a cli person to me, and the price for iperf is right (it's free).
One other thought to make sure the switch is not the problem is to get a 10GB crossover cable, and connect your two Macs together back to back. You might even get connectivity with a regular cable (that depends on if the Aquantia's have crossover support on their adapters - if they don't, then you might have to order a Cat 7 crossover cable - that might be challenging, but I just don't know about how well stocked your IT facilities would be where you are).
The final thought is also not great. I just touched my Aquantia, and yes, it was hot, but not as hot as you described yours. It is possible you might have a bad adapter. Hopefully not, but it's still possible. If you have to return one of them, I wouldn't worry about the flashing, etc. - most stores will just exchange it and throw the old one away, and even if they do test it, they'll do it on a Windows machine, and of course it will spit out garbage, and then it's just not worth the time for the them to waste pursuing what's wrong. Chances are, they'll just toss it....