How would the power not be increased by bi-amping? Your intergated would power the tweeter, and the power amp would power the woofer.
ATCs require a ton of power to open up. They're also ruthlessly revealing of anything upstream, so you need good components all the way through.
If what you bought doesn't do it for you, strongly consider ATC's integrated. It was designed to power them.
ATCs also need a good amount of space and SPLs to really shine. If the sound dull and boring, which is easy to do with them, something is amiss. With the right conditions, they're magical. Unfortunately, that's hard to pull off IMO.
I really wanted to buy a pair, but I couldn't afford to buy what they need to get them to sing. My 60 watt Bryston B60 fell on it's face. I wouldn't go lower than a Bryston 4B SST or ATC's integrated, but that's just me. YMMV.