I don't know. The new theme that I've been seeing as of late with these speaker makers is "8ohm compatible" which I find very suspect. I think what's really going on is that they're trying to ease the concerns of potential buyers knowing that so many people are buying lesser receivers to push these speakers with. People don't want to hear that they need to spend in the range of $1000 on a receiver to do their speakers justice, and speaker makers know that their products have to be more accessible these days. You have to be able to sell a good number of products in Best Buy and other larger retailers to make it since mom and pops have been disappearing in recent years.
Look at the Martin Logan Motion series speakers. Yeah...you can run them on a modest AVR since they're pretty efficient, but truthfully they are still 4ohm speakers that need solid power to open up and play loud. "8ohm compatible" seems to be catching on pretty quickly these days since I'm seeing many other speaker makers slapping that same label on speakers they know full well run in the 4ohm range quite a bit. Knowing what I know about Polk I would say an Onkyo 808/809 receiver is the minimum I would use on these speakers in any multi-channel situation. You could maybe get away with a 709 in a smaller room. If you are setting up a strictly 2-channel setup then most upper-entry to lower-mid level receivers should do fine, but again...in a multi-channel situation I wouldn't skimp. Polk makes some power hungry speakers and the LSi line is notoriously power hungry.
106" Motorized 16x9 Screen - Optoma GT700 Projector - Pioneer Kuro KRP-500M Plasma 1080p(living room)
Panasonic PX75U 50" Plasma 768p(bedroom)
Pioneer SC-05/Crown XLS1000 Amp & Martin Logan Preface Left/Right, Fresco Center, Sunfire HRS-12 Sub, Harman Kardon HKTS 11 5.1 sub/satellites = 7.2(living room) Onkyo HT-RC180 & JBL CST55/Energy Act6 5.1(bedroom) PS3 60GB and Xbox 360(living room) PS3 40GB(bedroom) Harmony One remote(living room)