To connect your turntable and tape deck to your new iMac computer using the UA-5, you may need to check if the UA-5 is compatible with your iMac's operating system. Make sure you have the necessary drivers installed for the UA-5. Additionally, ensure that you have the proper cables and connections set up between the UA-5, turntable, tape deck, and iMac. You may need to consult the user manual or support resources for your UA-5 to get specific instructions for connecting audio devices to your computer.