Additional Input device / router

Most of the preamps and integrated amps I'm interested in have a min. amount of inputs (some, like the Boulder, have only 3).  I want to know if there is an add on device (preferably high quality) that would provide additional inputs and outputs.  I need this in order to hook-up a cassette deck (please, no snickers) so wouldn't i need two outputs:  one for the device itself and one for the deck?  Does such a device exist?