My brother in NJ and I have been trying to connect on JamKazm. He's got his latency down, I couldn't with a brand new USB-C interface.
So, I pulled my vintage, decommissioned 2010 Windows 7 Sony laptop with Firewire, uninstalled about everything especially programs that would try and sync up with a mother ship somewhere like Amazon Music, Adobe, Google Drive, etc
I couldn't put both interfaces USB-C and Firewire on the same studio PC since the drivers conflicted.
This took a several days with uninstalling, updates from Microsoft and de-fragmenting the drives. Windows 7 is no longer supported by Microsoft but they updated it to the point of cut-off.
I connected my old Presonus Firestudio Mobile and the latency dropped from 16 ms to 4.3., a top line green light. When listening the sound was very scratchy and JamKazam recommended to lower the processor speed which makes sense for a 2010 laptop, a simple menu selection of low, medium or high speed processor, I chose medium and It cleaned right up with no loss of latency. It's hardwired to a 100mbs internet connection and gigabit switch.
I suspect that a USB 3/Thunderbolt interface would work well. The bottleneck/latency appears to have been in the transfer speed between the PC and the interface. USB2/C= 480 M bit/s, Firewire IEEE 1394b = 3.2 G bit/s, USB3 = 5.0 G bit/s, Thunderbolt = 10 G bit/s
If you have a desktop PC, you can drop in a cheap firewire card and buy used Presonus firewire interfaces at a good price since it's an old (but solid) technology. Presonus has an excellent driver, Universal Control. I'm sure other brands work well but some I've tried have not been very intuitive.
The Firestudio Mobile interface has (2) mic inputs and (6) line inputs so I have an SM58 vocal on channel 1, SM-57 acoustic mic on channel 2, Acoustic electric guitar on channel 3 and electric guitar on channel 4. JamKazm lets you add plug-in effects on each channel so I'm still messing with that. By brother has it working. Lots of free ones at KVR kvraudio.com/ to try out.
I have had reasonable luck with JamKazam, it does have some nice features. Interesting to see they finally got the plug-ins working, I'll have to check that out. I mostly have been preferring Jamulus of SoundJack. But they all work similar.
I suspect that a USB 3/Thunderbolt interface would work well. The bottleneck/latency appears to have been in the transfer speed between the PC and the interface. USB2/C= 480 M bit/s, Firewire IEEE 1394b = 3.2 G bit/s, USB3 = 5.0 G bit/s, Thunderbolt = 10 G bit/s.
While each user's set-up affects latency, the USB 3 isn't probably going to lower it much more than USB2; it's more about the other aspects and settings, like using ASIO. Those speeds are about how much data can transfer per second; is not the same as how fast. Single duplex audio uses very little data (like 192K/s per channel), far less than the capacity.
It is good to optimize your audio setup... usually not difficult to achieve fairly low interface to PC results.
But heads up - the main latency is almost always simply the connection between users; especially over the internet... the distance, the routing, data handoffs. These are most of the issue as to if tele-music is workable or not.
One great advice... pay less attention to the red/green/yellow or obsess on numbers; they are just rough guides, not always accurate... rather simply listen.
While for most folks, never going to be quite tight timing like sitting together in same space, some can be useable and fun; and there are some tweaks and aspects that can improve the experience, deal with latency.