I looked at a pdf of the user manual. It seems that there is a right speaker out, left speaker out, and a seperate din output for the sub. This would imply that it can work without the sub, and that the Tyros 2 provides amplification for the two sattelites.

Please correct me if I am wrong.
I am sure it will sound horrible by themselves. But remember that I will have a lot of bass from the main PA. Bass is omnidirectional...the main purpose for personal monitors is for the highs.