You could always try 7 up, it's pretty neutral. Amaretto would be best served alone, I think and Coconut Rum perhaps with pineapple juice.
I used to love amaretto sours. There are lots of commercial "sour" mixes.
What a delightful question.. i have to think about that one.. hmmm...ok how about orange juice with the coconut rum? I agree with the pineapple juice suggestion too. A lot of stuff is good in milk so that is also a good suggestion. Ever add anything to coffee? hmmm..
Great drink called a sea monster for the Malibu rum, it's a martini so equal parts: Malibu Rum, Pineapple and Hypnotique.<br />
Milk? As I am sure I have had Coconut Rum on the rocks with milk in it - was nice!