Slow down audio

Using Sonar porducer 8.5.  This particular song has only audio tracks (about 10 of them).  It was recorded at about 120 bpm - and the music pretty much follows that speed.  Well - after all the tracks are done - the writer now thinks the song should be "just a tad" slower.  I don't want to re-record everything - the chemistry was right on this.  What's the best way to slow this down without losing a lot of quality (willing to re-recod the vocals if I have to - but would rather not mess with the other 9 tracks)
 
Thanks
 

You would be better advised to use a mastering software suite to do that to the finished song. The plug ins that can do this with out to many artefacts are not cheap. 
Low end processing will trash your music ( IMHO) 
I drives me nuts that people ( the client)  think computers will magically fix anything. 
Explain to them that "yes I can do this if A- your willing to pay me $$$$ or B you don't mind the sound quality being diminished"  They will quickly be happy with the original. 

OK, I've been in this pickle many times. . . Here are some high-quality solid choices: . . Download REAPER for free, put your finished mix (or your individual audio tracks) into REAPER and just slow it down with the speed-control slider that is right there in the middle of the screen. This might be all you need because "a tad" slower might not be enough to spot any noticeable pitch difference. Yes of course it will be slightly pitched down, but I bet no one can spot it if you don't do an A/B comparison. I have done this MANY times in professional settings. Heck, it worked for the Beatles. . . If you are going to try the "TIME-STRETCH" thing, I suggest you find someone with Adobe Audition as this DAW seems to my ear and others to have the best audio-quality time-stretch. I've heard others say AudioSnap is good, but I am yet to find SONAR's as "artifact free" as Adobe's. ~Good luck!