One way to solve the problem is to increase your total bandwidth by plugging the USB 1.1 devices into a USB 2.0 hub.
All USB 2.0 hubs have at least one built-in transaction translator (TT) so that they can be downwards compatible. The TT automatically recognizes which USB category is connected on a particular port and translates any USB 1.1 signals to USB 2.0. There is a catch: you only have one TT for all your available ports, which keeps the bandwidth to the system down to no more than 12 mbit/s.
Overall performance suffers whenever all the devices on the hub have to share one transaction translator.
You can get around this problem by using higher-quality USB hubs that have as many TTs as they do ports. No longer do the devices on the hub have to wait their turn for some free bandwidth; the TTs optimally embed all the separate data streams in the USB 2.0 data stream.