I created an account here so I could reply to this guide. Thank you. It is excellent.
It took me many, many tries and no small amount of gold in repair bills, but as of today my fel flames are flyin'.
Each mini-phase of this fight must be mastered and there is very little room for error. After getting the first two imp/felhunter/doomguard phases down cold, I had issues late in the fight. First, the doomguards (one or both) would sometimes aggro on me. This was due to me getting excited toward the end and not gating enough. Also, don't forget that after the 2x felhunter phases, you are free