First off, I' dont want to tell you how to do things because obviously there are 1000s of users who like what you created (me included.. using jriver since version 7) But there are areas that can be improved so I'll give my feedback and you can ignore if you wish
Since all the media players seem to take ideas from each other...
What I would like to see in MediaCenter are easier menus (much like MediaMonkey)
I always laugh when I see MediaMonkey with a high rating on Download.com when it is 1/4 the program of MediaCenter
However, I will concede it has more intuitive menus. For example, I wanted to reorganize my music folder from Artist folders into Genre folders. I figured out how to do this with rename files from properties but it took a while to find out where to do this. I knew Media Center could do this because it does everthing but it took some searching... In MediaMonkey it is right on the main menu... Now this may be beacuse MediaMonkey does so much lessm, it easier to have "clean" menus
Also, my 2 cents (which i'm sure you dont want) is to rename your product. Ever since the OS was named MediaCenter and there is a buiilt in Media Center program in it, your program loses some identity. Frankly it gets confusing probably more to newbies who may not realize that your program is an separate and superior product
I dont know what would be a catchier name, but the current name is confusing and (JRiver's Media Center isnt so glamorous)