Center Speaker help

[ludawg23]

Just needed some clarification on a few questions that I had and was hoping you some of you guys could help.

I currently run a 2.1 setup at home with 2 floorstanding speakers and a sub, note that my receiver is capable of 5.1

Now, my gf recently complained that she couldn't hear the dialogue and that it was very low while we were watching Transformers on blu-ray

I have my ps3 set on PCM, receiver on Direct and I'm currently getting uncompressed audio but only in 2 channel.

Now, I have found a matching center for my speakers.

1) Do I have to be in a 5.1 channel mode on my receiver in order for the dialogue to come straight out of my center channel?
2) Since the PS3 cannot send multi-channel PCM audio, i'll have to set my PS3 on bitsream right?

I apologize if this doesn't make sense but just trying to see if I'll benefit from a center speaker and what settings I need to have my gear on for ideal performance.

Thanks.