My family owns the older Polk Rm6700 system because I used to work at CCity. With the discount, I think you'd be hard pressed to beat the polk system, especially if you can buy it without the sub and purchase a separate one (from velodyne @ ccity or preferably HSU, SVS, Rocket...).
The infinity i cant comment on, having never heard it. but, with the discount, the polk's will be tough competition in terms of value.
Remember you can always take them home and try them. most ccity's have terrible listening rooms. i found our polks sounded much better once we got them home.
Also, if you do decide between athena and onkyo, i'd certainly go with athena.