Working with Pro Tools files

I'm about to begin a project where drums, keyboard and bass will be tracked and mixed at a local pro studio.  I will bring files to my project studio to track and add guitars (jazz).  I will do the final mix and master using Sonar. The intended use for this CD is to sell (or give) at our local live gigs.  The pro studio uses Pro Tools.
 
My experience level is I did several local project studio CD projects about ten years ago using Cakewalk and Sonar up to about version 2.2, which all came out pretty darned well.  About 5 years ago I did a hybrid pro studio / project studio project, but I used Pro Tools (version 9) for Windows for my local project studio tracking and mix.  End result was good, but I did not enjoy using Pro Tools and really dislike their dongle and whole silly business plan, so I'm now happily back with Sonar Professional. 
 
My question is exactly what file formats to ask the Pro Studio to provide me.  To keep thing simple I think I want a good total combined stereo mix of the drums, bass and keyboard from the studio, but I also think I'd like a single stereo mix track of combined drums, plus separate tracks for the keyboard and bass.  
 
I'd appreciate any suggestions anyone might have as to exactly what to ask for and which file formats which would have easiest compatibility with Sonar Pro.  
 
Thanks for your thoughts and suggestions.
 
John Payne

I often record in Sonar and then use a studio that uses another program (MOTU Digital Performer in my case).
I normally just export everything as WAV files (that all start at 0:00:000"), although the studio recently told me that OMF files will include more of the project information.