No problem but with your old formation beware of 6 man MF's. they could cause you lots of problems.
Eg.
---------DC--DC--DC
-------DMC-------DMC
MR-------------------------ML
------AMR---------AML
-------------ST
OR
--------DC--DC--DC
DMR------------------DML
--------MC------MC
AMR------------------AML
-------------ST
Or even the 4-1-2-2-1 V formation
All will attack your flanks.
The SA defensive wall is only to block free kicks not players.
Next time you face 3-4-3 try 4-4-2 or 4-4-1-1 with red arrows on your MR/ML, I'm sure you will like the result.
3-5-1-1 is also a good attacking formation.