Hi all,
I have always payed the taimanov via the 5…Qc7 move order, seeing 5…a6 as the solid but passive option, mainly because of 6.NxNc6, but I’m not so sure now. 5…Qc7 leads to more direct play and is nowadays full of forcing lines. It is still very reliable but against some systems, the reliable solutions have become limited and not always to my taste, particularly when I want to avoid early simplification. For instance, the systems with g3 or the trendy Qf3 offer little good choices to play for a win, in my view.
So I reconsidered the move order 5…a6 as an alternative, just to see if when you accept to allow the 6.Nc6 positions, you get some potential reward. I started a list.
The “rewards”:
Nb5/ You obviously avoid all the Ndb5 or Ncb5 stuff.
Qg3/In some variations, the trendy maneuvers to propose a queen exchange on g3 are pointless.
  Qf3/ You can get options against the annoying Qf3 system like 7…Bb4 or 7…d6 which according to Illingworth in Dismantling the Sicilian is much more interesting with the queen still non d8.
English attack/ You can neutralize the English attack with an early d5 and Bb4 or transpose into it only after having avoided the lines with f4.
g3/ You can play systems with 6…Ne7 (original Taimanov idea) or 6…Nd4 and then b5 against 6.g3 or you can transpose into the Scheveningen much more easily without an early Qc7.
Be2/ You can transpose into the Scheveningen without Qc7 against Be2.
Be3+Bd3/ You can play immediately d5 or e5 against the “third rank set up” as called by Semkov and Delchev.
This is starting to look very interesting to me.
For all this stuff, the “price to pay” is
  The 6.Nc6 system, with pawn particular structures which are not to everyone taste but keeping a complex strategic game.
  You allow 6.Bf4;
  You allow this “dangerous weapon” from the old Everyman series: 6. Be3, Nf6 7.f4, but it seems neutralized in various ways. Notably with Bb4 followed by e5.
Given all these nuances, one can benefit from having both move orders in his repertoire to confuse opponents or to give either a forcing tactical or a more strategical  flavour to his taimanov.
The more I look at it the more consider the nuances between the two move orders is a fascinating subject, but there are no sources on it I’m aware of (the a6 Taimanov is completely neglected).
So, I propose to start a thread on it. Feel free to complete my lists (“price to pay” or “reward”) or to expand on some points.