Wow, you have a varied mix of B&W speakers from different model lines. I was hoping that you were going to come up with some B&W Silver Signatures but that's the way it goes. The pictures below are what you have, right?
The DM610 speakers are from the original 600 series and were made around 1992. The MSRP at the time was $500 a pair. They have large 8 woofers and are hard to drive at 4 ohms - these are the speakers that had the board and wires cobbled together by your friend, right?
The 2000IFS center speaker is from the 2000 series and was made around 1994. It has two 6.5 woofers and is intended as a center speaker. By the way, it is not a subwoofer.
The DM302 speakers are from the 300 series and were made around 1996. The MSRP was $250 a pair at the time. They have a 5 woofer.
The spec sheets from the B&W archive are here:DM6102000IFSDM302
With this setup, I imagine a surround system would look like the DM610 for the front left and right, the 2000IFS as the center speaker, and the DM302 as the surround speakers.
To be completely honest, these seem kind of tough to work with because they are so mismatched and the DM610 are so big and you don't seem to want that. The front three speakers should be from the same series to make a sonic match. Imagine watching a movie and a car moves from left side of the screen to right. The audio will match the picture and the sound of the car will move from the left speaker - to the center - to the right speaker. If the speakers are too different the transition will sound strange, maybe even distracting. That's what you have going on if you put the DM610 in front with the 2000IFS center speaker. It's almost impossible to find matching speakers for these now.
I think you got your money's worth out of these but it may be time to move on. What do you think?
Since you realize that the tiny Sony speakers aren't as full as the B&W, you might want to consider something other than the tiny Polk speakers you were originally looking at. You can find some speakers that will sound better.
I can run a few past you (maybe using the DM302 as surrounds, maybe not) but I'd need to know a little bit more about what you really want.
-What percent do you watch movies/TV/music? (for example 40/40/20%)
-How big is your room?
-What kind of components do you have? (LCD TV, cable box, DVD player, etc)
-What's your budget and for what? You started with an Onkyo system that included a regular DVD player but later you said that you wanted a Blu-ray player.