Question

Can I connect my firestudio mobile to a studio 6|8 to get more interfaces?

Answer 1

The FireStudio Series had a unique feature that allowed you to add more FireStudio devices to expand your I/O, this is not possible using the USB Audio Studio series interfaces, you'd need to use another FireStudio device. As the FireStudio line has since been discontinued, you may be able to find a 2nd hand unit to use.

Consider moving to a larger single interface that offers the amount of I/O that you're looking for.