Sorry for the delay. Work picked up to a pace I haven't seen in months. That's a good thing. Now, back to the review.
I'll break this down with a simple pros/cons of each of the bookshelves in the A/B comparison. Again, they are the Insignia's at BB for $39.98 a pair, and the Polk RTi4's which retail around $320 a pair. They are being driven by a Denon 3805 AVR in 2 channel mode, so there's plenty of headroom.
Polk RTi4 Pros:
Big sound, small speaker - can fill a large room
Excellent mid bass from a 5.25" woofer, very punchy
Handles big power, and plays loud. Does not distort
Accurate, Detailed
Nice build quality - heavy speaker, huge magnet and crossover
Smooth midrange due to the smaller driver and large 1" dome tweeter
Outstanding customer service and great warranty-5/5 parts/labor (Polk)
Polk RTi4 Cons:
Very deep cabinet, not a great wall mount design
Lacks the lower bass notes (65Hz and under)
Same grill as entry level Monitor series
Hefty price tag
Some may say sibilant
Insignia Pros:
Sexy design - triangular to reduce resonance
Very good build quality
Impressive carbon fiber driver, huge magnet
Outstanding imaging
Very strong midrange (see below)
Excellent speaker for classical music
Looks best with the grill off
Dirt cheap! Buy 6 for $120 - you can outfit a start up HT room under $500
Insignia Cons:
Rolled off highs, very weak bass (not much under 100Hz)
Distorts at moderate to high volumes, especially the bass
Bloated midrange, needs eq'd down in the 800-4000Hz range
Not impressive with movies, does better with certain music
Very large bookshelf, too large for shelf, and no easy way to mount as center
What to do if you blow the driver - are they hard to find? How much?
Weak warranty - 90 days parts/labor
Some say a knock off of a knock off (Kef -> Radiiant -> Insignia)