Bandwidth means not enough cpu power or usb channel speed?
It is the usb bandwidth. The host controller channel to the usb device does not have enough capacity for the requested video stream. The Bresser microscope asks for 8 times 3 times 1020 data bytes per microsecond. That is 24.480.000 bytes per second not counting any transmission overhead. I don't know what the other webcam asks but together it could not be delivered. I don't recall what maximum data rate can be delivered. When you have more than one high speed high bandwidth host controller then you could connect the cameras to different host controllers.
I could send my latest version of usbcalls.dll and usbresmg.sys for you to try out. I'll send it to your private email address that I have. I rather not post it here because the proper documentation is not finished yet. So you'll have to keep it to yourself.
I finished implementing the USBCALLS - REXX/2 External Functions. The USBCALLS - REXX/2 Reference Guide is now included in usbres04.zip available on hobbes and on my website http://home.hccnet.nl/w.m.brul/usbcalls/usbres04.zip