1st of all , I wouldn't go with the MC cable ( metal ) , unless you plan to use metal junction box,s . MC is made for commercial applications where the studs are metal . If you dont secure the MC cable with red eyes and the proper connections you could have problems later , as the wire will slide inside the metal jacket , and over time you could get a dead short . Here is what I would do . I would go with a 20 amp single pole breaker ( make sure the breaker matches the panel ; IE , square D , G E ) . from the panel I would run a 10/3 ( romex ) . This means the wire is a 10 gauge with 2 hots , a nuet and ground ( with out being there and doing a code calculation , I would just use # 10 ) . One of the hots will become a nuet . Take the extra hot and put white tape on it inside the panel . Now inside the panel you will now have a hot which will go to the breaker and 2 nuets and a ground . pull to 1st junction box . Inside this junction box you now isolate the wire you put white tape on inside the panel , make this white with tape . So now inside your box you will have 2 nuets and a hot + a ground . On one nuet share the humidifier and light , and the other nuet goes to the Recept . This way you have a dedicated nuet to the stereo . Gary mentioned a 30 amp breaker , when you get into this size the recept almost always will be a twist lock type at the recept . The bottom line is that from the panel you want 1 hot and 2 nuets and a ground . You want to isolate ( nuet ) the humidifier and light from the stereo . Hope this helps , PM if you have any questions .