MTH Railking with Lionel System

Need some help.  I have researched past forum discussions and can not find any recent information.  

I have a vintage Lionel set-up.  KW transformer and tubular track.  I bought a Lionel Lionchief (Polar Express for my grandson) and found it easy to use.... works great. Now looking at a MTH Rail King with ProtoSound 3.  

My question(s) are - 1) Is this a good idea to begin with considering my current set up. 2) If purchased how difficult is it to use the Railking.  

I have done some research or at least tried to and what I found was dated.  And I cannot figure out the MTH website, which to me seems to be poorly designed. 

As always .... thanks in advance for your assistance.....

Tucker