I am fairly new to TAXI and Sync in general (3 months in..), and have approached this in a couple of ways so far...
1.) When I started on here and didn't know any better, I would simply take an existing SONG (not cue) of mine and submit it to a brief that asked for a particular genre.... I typically would gloss over the ref tracks, and think to myself "Well, my stuff is soooooo good, that it will get forwarded anyway" - WRONG. You can waste $5.00 per submission for the rest of your life as this almost never works.
2.) Then....After listening to several folks right here on this forum, I started to really dig deep into the ref tracks.... First thing is matching the tempo, Second thing is to note the structure of the track, and the key, etc.... Third thing is to listen to what instruments and tones are being used. While I have never thrown the actual ref track into my DAW, I will keep a Youtube window open while I am working so I can go back to it quickly. Now, I did have one track returned recently, because a riff was far too close to the reference, so it MUST be different...You cannot copy it whatsoever.... I change the key, and try to change every single note, chord, melody, etc, so as to make it unrecognizable to the reference. They are not looking for "soundalikes" (at least the listings I have seen so far..) THEY ARE LOOKING FOR THE SAME INSTRUMENTATION and VIBE.
3.) Triangulation of several reference tracks. This is the tried and true method that I am currently working on, and it is not easy.... Sometimes the ref tracks are completely different from one another, which makes this difficult to do IMHO, so in those cases, I tend to lean on method #2 above, and submit several tracks BASED ON (not copying...) each reference track.
And as far as reference tracks containing vocals?? This does not seem to be an issue for me...... Note the vocal melody perhaps, but otherwise I really do not pay any attention to them, other than using vocals as a guide to where the verses, bridge, choruses, etc are in the song.
And finally.... USE MARKERS in your DAW. I tend to have all sections of the track counted out and set up before I record anything. You can always add or get rid of stuff later, but have a blueprint to work with in the beginning..Anyhoo...Thats my two pfennigs!