They are also unused so I am thinking about filling them with some bourbon or wine first to get some of that flavor in there. Thoughts?
Good idea. You'll be doing a few things to set yourself up for success:
1. You'll be getting some of the barrel newness out
2. The barrel will be sanitized by he absorbsotion of alcohol into the first layers of wood
3. The barrel will be leakfree when you are ready to add beer
4. Beer will pick up both wood and alcohol flavors
This might be a bit of a longer project than you anticipated by first aging some whiskey in the barrels but in the end I think you will be happy with it. I would start by filling with hot (180F) water and making sure it is leak free and allow the wood to swell. Then dump and add your spirit of choice. If you want to see the affect on the spirit use a white or unaged corn whiskey and you can watch it darken over time.
Best of luck. I am on my third barrel aged beer (imperial Porter, trippel, and Dubbel) and have had great success with a 10 gallon and 5 gallon barrel.