That was 45s, not 450s. It was more dreaming of a nice setup using current model def tech bookshelves with a sub. If you went with the older studio monitors, I would recommend 350s and finding the clr 2002 on a search of all craigslist and finding someone willing to ship it.
As to sticking with Polk, I thought I mentioned above that the monitor 40s were the best match for your current center. Since you are using subs, I expect you would get near identical to current sound quality. Those use the exact same drivers and tweeters as your towers and center. It would certainly be your easiest solution changing the left and right and selling the towers as opposed to all three. If you don't mind selling all three the sm350s and clr 2002 would probably be a little step up.
Either way, newegg has good prices on either pair of bookshelves. What you get there will determine whether to keep the center or sell it and look for the used def tech.