Guardians of the Orb - Idea

I'm going to start this off with a small encounter idea. I have 2 PC's, so this has to be a slightly scaled down encounter. It's meant to be a fun, fairly easy encounter where the PC's have to use some strategy but they get to kill a lot of monsters quickly.

Story:

The PC's are sent to recover a magical item called the Eye of Ioun. You could replace the Orb with any magical item that fits your story. The Orb is guarded by a couple of guardians that attempt to stop the PC's from touching the orb. The concept is that these are large golemn like stone guardians, most likely soldiers.

Once the PC's touch the Orb four hidden doors slide open and they are mobbed by a wave of minions that try to stop the PC's from leaving with the Orb.

To help make the minions easier to take out the room will have a couple of crystalline "blasters" that will allow the PC's to send out a blast to take out the minions en mass.

So, there is the basic idea, I've sketched up a map which I'll upload in part 2. Do you have any ideas, tips for making this encounter good/better, any suggestions for monsters to use?