The A7s are the higher line, more resolved and better for HT. However, your center is a TSi and will be overpowered a bit. The best matching center for the A7s is the CSiA6. Even with the 500s I'd recommend the CS20 vs the CS10.
and if you are considering the TSi lineup, the older Monitor series are basically the same speakers with an older enclosure style. TSi 500 = Monitor 70, CS10 = CS1 www.newegg.com has extremely good prices on the Polk Monitor Series II speakers. The Monitor towers that match your CS10 center are the Polk Monitor 60 towers.
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