Center Channel Decisions!

Hello!

          So ever since we got Netflix, I've been ordering and watching many more DVDs than usual. Earlier this year, I got a pair of PSB Image B25s for my birthday (Specs Here). My next purchase after saving for a few months was a pair of Martin Logan Motion 4s (Specs). Craving more low end for movies and certain genres of music, I got an EXTREMELY good deal on an Energy ESW-C10 subwoofer, which is an amazing value for $325 off  (Thank you ebay!). All speakers are powered off of a Harman Kardon HK 3390 stereo reciever, with the sub pre-out obviously leading to the sub.

          Knowing I am not using all of my speakers in their ideal way (currently 4-way stereo), I realized I could upgrade to a mini home theater in my room, for not much cost. All I would need is a center channel and a surround reciever. For the reciever, I was looking at the Harman/Kardon AVR 1600, mostly because the 3390 made me fall in love Harman Kardon's looks. To afford the AVR 1600, I would sell my current reciever and my Logitech G25 which is collecting dust. This leaves the center channel.

            Now, the main reason I mentioned my speakers is because each speaker I own has a corresponding center channel it its series (PSB Image C40 centre is part of "Image" series, and Martin Logan Motion 6 centre, which is part of the "Motion" series). So far, in my 4 way stereo setup, the MLs are in front, with the PSBs on stands behind me. Knowing I can get the Image C40 center and the Motion 6 center for the exact same price, which should I choose? I'm assuming I would put the PSBs in front if I purchased the C40, and keep Motion 4s in front if I purchased the Motion 6 for synergy reasons. 

             So, let me rephrase my question, hah: Which speakers should be fronts, and which as surrounds, and which center should I get?

             The dramatic differences between the speakers are that the PSB clearly has more bass (not sure how important that is with a sub though), and the MLs have brighter (better in my opinion) treble. They are both fantastic for music however.

Miscelanneous stuff: Size is not too much of a factor, the C40 is 23 inches long while ML is 17. Also, this setup will be used for about 70-80% music and 20-30% movies, depending what day it is. If you need pictures of my current setup, I'll gladly post them.

Thank you for your opinions! It is much appreciated  Sorry if it's a confusing read 

-Evan

Oh the C60 makes more sense for matching my B25s, you're right! However, would you still recommend it for a small room? 

Room is 12x12 and the speakers are set up in about 7x8, due to space constrictions.