Thanks for the great thread everyone. Ordered PCI card and will give it a go. My concern is internal USB connectors - like the WiFi/Bluetooth PCI card that needs internal USB or the Thunderbolt 3 AIC card that also uses internal USB. AIC card is probably USB3 though, so should be fine.
FWIW, It proved impossible to do this for me. My issue couldn't be traced to a single device. Every time I thought I had figured it out time proved me wrong. I THINK at one point it was freezing with just a kybd and mouse plugged in (maybe it was my expert mouse trackball or old lenovo keyboard???). The only 100% freeze proof solution on my system was to use the card for all USB 1&2 devices. That said, once I had stability I stoped chasing the problem.I think you just have to isolate the devices that are causing the issue and keep them on the PCI card ports.
FWIW, It proved impossible to do this for me. My issue couldn't be traced to a single device. Every time I thought I had figured it out time proved me wrong. I THINK at one point it was freezing with just a kybd and mouse plugged in (maybe it was my expert mouse trackball or old lenovo keyboard???). The only 100% freeze proof solution on my system was to use the card for all USB 1&2 devices. That said, once I had stability I stoped chasing the problem.