does using many usb 2.0 input makes the audio quality any bad? because I am using 6 usb input in my laptop through usb audio interfaces, keys , sonuus and other devices. I doubt it might lower my audio quality.
Generally no, using multiple inputs shouldn't lower quality as long as the USB controllers still have sufficient bandwidth for the devices to function. If you use a hub to connect everything, then you may run in to data rate issues causing latency or outright failure, but in general, the data is digital and should get from point a to point b alright.
There are exceptions and caveats though. If you are using multiple USB capture devices for example, then unless you have a word clock hooked up between them, USB doesn't provide good syncronization of clocks and you may get some timing differences between the two interfaces. For anything other than pretty high end work it should be pretty minor in most cases, but it is one disadvantage over a single larger interface or higher end interfaces that have a word clock sync cable.