I was surprise by the score as well, but I was on the back of 4
straight victories and the morale in the team is high. But to beat
(not to the extend of thrashing them, maybe it was just one of
those rare cases) Barca at home you have to exploit thier
formation. In my game Rijkaard likes to play a 4-5-1 normal
formation.
They have 4 defenders, 1 defensive midfielder, 2 midfielders, AML
and AMR and finally a lone striker.
Attack Side - I found out by watching their other matches that
their full backs like to bomb forward and that they have only one
defensive mid. So I used two AMCs to overload the lone defensive
mid, and my two AMCs' arrow point to the AML and AMR position to
exploit the gap left behind by the full backs. My AMCs run with
ball often, cross ball often as well as try through balls often.
Pressing is mixed to the extend of often. Cross ball to area put
centre. My Torres run with ball often and forward runs often.
Creativity level put normal to the extend of little, you wouldnt
want your strikers to try too much to create, let him do the
scoring solely. Torres does near to often pressing so that if a
defender dwells too much on the ball, he will be able to disposse
him.
Defensive side - Knowing that Xavi and Deco are super creative
players, I put 3 defensive mids with pressing to the extend of
often to try to close down the space. My DMCs plays direct balls
with normal creativity level to the extend of little so that they
only do simple stuff like playing a direct ball to Torres when
there is free space. They cross often to centre area as well. My
DMCs cover the left and right flank as well as the centre area. All
my players use tight marking except Torres to restrict the space
and time players like Messi and Ronaldinho craves. Rijkaard played
Etoo as a lone striker and does not call him to fall deep to
retreive ball, therefore he is easily dealt with Pablo who has
great positioning, strength in the air and reasonable pace as well
as Perea who has great pace.
But well this is just some part of my tactics, cant possibly typed
everything out. These settings are not perfect nor is my
formation.
There are still more improvements to be made regarding my formation
and settings and the above tips are just my opinion. Fellow FM2006
players out there may beg to differ 
