Teac NT-505 Firmware Upgrade Help

Got the Teac NT-505 streamer and very pleased with the sound, but I cannot get the device firmware update to work.  It shipped with Ver 10 firmware (which was actually the second firmware version), and the current (latest, 3rd) version is numbered Ver 21, which is the one I can't get to load.

Teac NT-505 is old school, meaning no slick network updates like modern kit.  Instead, you need to use a PC (no Mac) and download a zip file, unpack it, and then send it to the NT-505 by a micro USB cable from the PC.  I was apprehensive about this going into the purchase because so used to the simple way to update modern components, but went ahead anyway.

Downloading the update, unpacking it, and everything else seem to be okay on the PC, until such time as I connect the USB cable to the Teac and hit go...   What happens when I try to update is the old MSFT DOS-looking text window pops up on the PC and it says the update didn't work because device not recognized.  

Questions for those who have successfully updated to Ver 21:
1) Must Teac NT-505 be connected to network (Ethernet) at time, or is only micro USB cable needed?  Instructions don't mention anything about needing Ethernet access.  Reason I ask is I've tried with home laptop with Teac hooked up to network (didn't work), then brought Teac in to work where no Ethernet connection available and didn't work with second computer either.

2) Is the phone app involved in any way in the upgrade?  Instructions don't seem to mention phone app at all for this.

Any advice appreciated.

By way of review, I can compare the Teac to Marantz SR5012 AVR and Integra DTM-7 stereo receiver, both of which I have in separate systems, and the Teac sounds better (as it should, costs a lot more).  Streaming Tidal on all.   But this upgrade thing is driving me nuts ...

Disclaimer on comparison: running Teac thru ARC DSI200 integrated so not an even apples-to-apples comparison with either Marantz or Integra, cost-wise.  Between the Marantz and Integra, I prefer the Marantz.

Happy ending. Dealer was able to do the upgrade. Turns out I’m an idiot as I was using the USB labeled port on rear and not the unlabeled micro USB port buried near bottom. My bad ...