I actually did this back in February - Pravana Purple over about 6 months of burgundy dye. Boy was my hair PURPLE.
I became really sick of the tub being stained purple, so I used Loreal Color Zap from Sally's Beauty Supply to remove it -
L'Oreal - L'Oreal Technique - L'Oreal ColorZap Haircolor Remover
It took one application and my hair was bright orange. It was enough for me to dye over it an ash medium brown color that looked fairly decent. Still came out really warm looking, but it was no longer burgundy or purple. No one knew the difference!
I didn't use Color Fix because it's never really worked for me before. The second picture I included was the color after about two weeks. It was much warmer in real life, but still decent looking. And I had removed A LOT of red tones from my hair underneath the purple.