Stem files sent online from anywhere in the world can be Mixed professionally in California and sent back to you fully Mixed and ready for Mastering.  Specs for stem files are:

Wav Files.
48 kHz Bit Depth.
24 Bit Rate.
(If recorded at a different bit depth and bit rate than 48/24, turn your files in the same as you recorded them, for example 44.1 kHz, 16 bit, or 44.1 kHz, 24 bit.)
All Files Starting at 0 exactly (left edge of project).
Minimum of 1 Second of Silence At Beginning of Overall Song.
No Fade Outs - Let The Song Run Until It's Over.
Ample Headroom. 

(NOTE: Headroom does NOT mean the level of your file - the level is really unimportant.  You might turn in stem files that average -6dB to -12dB of "headroom" -- which most mixing and/or mastering engineers ask for - but if the stem files or the the mix are overly compressed and/or limited and if the DYNAMIC RANGE has been squashed [dynamic range is the difference between the loud and soft sections of the music] then it doesn't matter at what level you turn your tracks in - the important thing is that there is little to no noise on the track and that you have preserved the Dynamic Range of the track.  Of course, no audible clipping or unwanted distortion.)
 
Each Stem File Broken down by Separate Instrument/Vocal.
Each Track Dry as well as same track with your effects - Both are needed.

Files can be sent by YouSendIt.com (if you don't have an account you will be given access to ours). For more information and for Mixing rates write to gary@SculptorOfSound.com