RBR750 large downloads choke all other connections

I have an iMac Pro I work from home on, and my wife works on her laptop in another room connected to the satellite unit.  I'm finding that when I start a big download (100s of MB or more) specifically from a browser, but sometimes also software updates, not only do all my other network connections die off, but even open tabs within that browser refuse to load as well.  I have a work VPN which connects to Microsoft Remote Desktop for one of my work machines, and I use Chrome Remote Desktop to connect to the other one.  This arrangement works perfectly fine, everyone has internet, all browsers (at least two separate ones) open on my iMac have no issue with network connectivity.  I can even do a zoom meeting with all of this open, and nothing seems to suffer.  My main internet connection is a 100Mb fiber (100Mb both up and down), so I'm pretty sure it's not a bandwidth issue.

When I initiate a large file download from a browser, the VPN connection dies off almost right away, followed by CRD.  If it's not TOO big of a download, sometimes they will re-connect when the download finishes.  If I'm doing an OS upgrade (upwards of 15GB download) or something especially large, sometimes the satellite unit starts dropping connections.  This has become more and more cumbersome lately, as I've been needing to download files for work, and then I have to re-connect my office computers when the download finishes.

Digging around on the community posts here, I found reference to http://orbilogin.net/QOS_main.htm which is supposed to help me set up QoS on the router.  I will say this page does absolutely less than nothing and I'm not sure why it exists.  Clicking on the text on that page gives me a pretty detailed help page at the bottom of the window, but literally none of that stuff comes up when I click on "Turn on QoS" (see orbi-RBR750-qos.png attached).  I can't change settings, because one of two things happens.  Either I get taken to a speed test page with no way to get back to the QoS settings, or I get an error "Invalid uplink bandwidth" (posting inline here):

I feel like I should be able to change these settings, or at least to be able to start large downloads without something deciding to devote the entirety of my network resources to getting that file, and ONLY that file, and abandoning all the currently open connections as a result.  I've just about had it with the Orbi system, to be quite frank about it all.  I'm currently looking around to replace this system, because this is kind of ridiculous how I can EITHER do a big download OR work, but I can't do both together.