I am interested in the Eclipse AVN7000 - to replace my factory NAV system in my BMW X5. Is this the best option for NAV? Is there an In Dash option (I think the car only has single DIN - but I certainly am no expert). Will I be able to use my steering wheel control for volume ect? Thanks for the help!

With enough money, anything is possible... I am personally not extremely familiar with your x5 or the eclipse, but it should be able to work for a little extra money for some converters.