Dimitre, 

The lower launch could be the only reason you may be losing carry distance.  Two clubs short in distance is a big difference and would take a significant lower launch and added or lack of spin to cause this.  The lofts should be the same, but it wouldn't be a bad idea to check them out and make sure they haven't been altered in any way.

Cameron

1-888-TITLEIST

According to the charts at Golfsmith, the KBS Tour 90 is a low launch shaft and the Dynalite XP is a high launch shaft.  The iron performance guide states the CB is low trajectory iron and the AP2 is a medium trajectory iron.  Dynalite Gold is a heavier shaft (117g vs 95).   Also, one vendor's "stiff" shaft may be another's "regular".      

1.  Low launch shafts roll more.  That alone can be a distance difference.   Do they carry about the same? 

2.  Given the same swing weight, lighter shafts give a slight increase in swing speed.  Not 20 yards diff, though.

3.  Hitting a blade iron (MB or CB) is slightly different vs hitting an AP1 or AP2 (same analogy with X31 vs Eye 2).  The blade is designed for hitting down on the ball and the latter is more for a sweeping swing. Try using more spine tilt with the AP2; it also takes advantage of the high launch shaft.  Back in the good old days of Golf (when the only clubs were blades), we were taught to address the ball with the hands way ahead of the clubhead and hit down on the ball.  Trying to hit down with an AP1 or AP2 would kill the clubhead speed at impact  (TT members pls chime in; don't claim to be an expert on this).  When I had X31s, I played my 5 and 6 irons near center and I play about a ball ahead of center with my AP1 7 iron.

4. There are also some flukes.  For instance, I had some Eye 2 irons with mixed shafts (I ended up reshafting to TT Lite XL R flex).   The 7 iron had KT-M stiff and the 8 iron had DG X.   I actually hit the 8 iron farther by 3 yards (mainly due to roll) but the launch monitor showed a 25 yard gap and the 7 iron had a tighter pattern (when I reshafted, I got the 10 yard gap back and an increase.

Obviously, going from CB to AP1 doesn't require a 360* full blown fitting; however, it would have been prudent to do a side by side using a launch monitor with the CB iron and one of those from the fitting cart.  "Apples to apples" would have been the KBS Tour 90 shaft on each and then try different shafts on the AP2 or adjust your swing a little.  

I pretty much know that either DG R300, DG HL R300 or TT Lite XL have worked.  I've tried KBS C Tour shafts alongside DG R300 on a P**g fitting cart and found them about equal for feel. 

This is considering that one is spending $1000+ for a set of irons.  Just my two pennies.