hifi engine

Connect Marantz 4240 and Music Streaming Device

Hi everybody, I am the happy owner of a very old Marantz 4240 receiver (purchased 1974!) and an equally old turntable (Thorens). They reside in one corner of the living room and we use them for playing old vinyls. Sice I am fully computerized, I have done the following:
rip all my CDs and have them on an IPod compatible external disk (possible NAS!)
I am now planning to purchase an audio streaming device and fully integrate it into my WLAN network
finally both the very olsd Marantz/Thorens combination as well as the new Music Streaming Device will rest in my hifi box in the living room

Rather then having two sets of load speakers I want to integrate the Marantz/Thorens and the Music Streaming device. I assume there are simple switches existing, where I can connect/disconnect the load speakers to the oneor the other. Are there otherways of connecting the two "worlds" to eachother? Thanks for helping, Heinz