pci express - Possibilities to increase overall USB 2.0 devices throughput with PCIe expansion card

I've checked most of the U3/U2 bandwidth questions on-line, but still have some confusions.

I understood that, if I had one USB 2.0 controller and one USB 3.0 controller in my laptop, even if I plugged my two bandwidth-consuming USB 2.0 devices (both needs 250Mbps) separately to both controllers, the two U2 devices still share the Hi-Speed (480Mbps) from the USB 2.0 controller (xHCI).

If I added one "PCI Express USB 2.0 expansion card" with 2 ports (dedicated controllers), do I get total "3" or "2" or still "only one" Hi-Speed (480Mbps) throughput?

If I added one "PCI Express USB 3.0 expansion card" with 2 ports (dedicated controllers, e.g., μPD720202), is it helpful for my scenario? Can I get both U2 devices with 250Mbps, one plugged to the original laptop U2 port and ont to the U3 expansion card? I'm asking this is because I saw these kind of U3 expansion card claimed with the compatibility of USB 2.0/1.1/1.0, and I'm wondering if it can act as an independent USB 2.0 controller, or just route to the xHCI of my laptop.

Additional question: If I disabled the built-in xHCI of my laptop, and just use such PCIe USB 3.0 expansion card, can I still use my USB 2.0 device with its port? If the answer is yes, and there are two ports (with dedicate controllers, let's say μPD720202 *2) on the interface card, does it mean I can plug both my 250Mbps devices to it as it being two independent xHCI ports?

Thanks!