Between the two amps go with the infinity. I personally wouldn't go with an infinity amp, but i don't know what your budget is. Check out ebay, you can find some pretty good deals from online stores.
how about the 75 watt per channel memphis amp? It would then match the 500 watt amp for my two Adire Shivas. I personally have not heard very good things about infinity, but right now the 100 rms amp can be had for $99 at an online retailer. The memphis is $180. Cost aside which one do you think would be a better choice?
I've never heard or have had any experence with memphis, but i've heard they are at least durable and trustworthy. Cost aside the memphis is probally better, yet you are still under powering your 6.1's, and you might be happier if they were getting their necessary power, even from a lesser quality amp. Now, don't get me wrong I love infinity, but they are good at highend speakers and subs, not amps. OR I know you said a new memphis would match your other, but you could also look at cadence, jbl, kicker, or mtx. They are all in about the same price range.