Not sure if this has been posted yet.. but I found a great table that shows what L/R speakers matches center channels. I got it off the Polk Audio website.
What center speaker matches my older Polk Monitors, RTA, or SDA loudspeakers?
While Polk speakers have evolved and improved over time, some basic "signature" Polk sound traits have remained constant. Clear, projected midrange, open, airy highs and wide soundstaging are all hallmarks of the Polk sound, past and present. Therefore, Polk center channel speakers are the best match for older Polk main speakers.
The CSi5 makes a great match for top-of-the-line Polk speakers of the past such as the legendary SDA-SRS. It is a large full range center channel speaker that works superbly with larger Polk Monitors, S Series, and RTA models as well as all SDA loudspeakers. The LSiC is a great match for LS Series Polk models from the 1990s. The CSi3 matches well with mid-sized mid-sized Monitors (5jr., 5 & 7), S Series and the RTA 8. The CS1 is perfect for the smaller Monitor and S Series models.
Find your vintage Polk model on the chart below to see which center model is the right choice for you. If you can't find your main speaker model on this page, or require help of any sort, contact Polk customer service.
Center Model - Matches With:
LSiC - No vintage matches.
CSi5 - SDA-SRS, SDA-1, SDA-2 (all versions), SDA-CRS, RTA-15, RTA-12, RTA-11, Monitor 5, Monitor 5jr, Monitor 7, Monitor 10 and Monitor 12, LS90, LS70, LS50, RT20p, RT16, RT12, RT10, RT3000p, RT2000p, RT2000i, RT1000p, RT1000i, RT800, RT800i, RT600, RT600i, RT55, RT55i, RT35, RT35i, AB855, AB805, AB800, AB755, AB705, AB700
CSi3 - RTA-8T, RT8, RT7, RT5, RT15, RT15i, RT25, RT25i, Mini Monitor, "Monitor", Monitor 6 satellite, Monitor 4
CS2 - R30 R40 R50, S8, S6, RT400, M5
CS1 - S4, R1, R2, RT3, R20, R15, R10, M3, M3ii, M2, M1