The speaker choice has to depend on your listening environment. For example, since the 1604 has a relatively low power rating, you need to use efficient speakers with sensitivities in the mid-90s or higher. Speakers with lower efficiencies won't be able to come any where near THX reference levels if you're seated at the usual distance of about 10ft (3m) or more.
Paradigm Atoms typically have sensitivities around 86dB. That's OK for quiet music, but inadequate for movies in your room.
Interesting. I've never really look much into 'matching' speakers with my AVR, but now you have me interested in researching more about this. I currently have two Anthony Gallos Micro speakers, but they are only rated to 89db. Are you saying these wouldn't be taking full advantage of my AVR?
It's not that you're not taking advantage of the AVR. A few 10s of watts is almost irrelevant.
Inefficient speakers (< 90dB) with a low maximum wattage (<250W) are unable to provide movie reference sound levels (105dB) at a distance of about 10ft (3m) without distortion or potential damage to the speakers. For full volume (THX reference level) with the 100W provided by most current receivers, you need speakers with at least 96dB sensitivity.
A detailed discussion of this is currently in progress in the Audyssey thread, starting at about http://www.avsforum.com/t/795421/official-audyssey-thread-faq-in-post-51779/67890#post_24065997