Can anyone tell me if i can use a d16a6 (si) intake manifold to replace the intake manifold on a d15b2 (dx)? The d15b2 manifold has the black circular looking dual-point PGM-FI. The Si is the silver smaller tubular manifold.

 

Yes, that is called a DPFI to MPFI swap. You're going to need to do some minor rewiring as well as get the right ecu and some other parts. This has been covered millions of times, so I'm sure if you do a search (upper right-hand corner), you'll find more info than you can handle. Good luck!