I just had these Focal components (IS 690TOY) installed, along with a Memphis Audio 10" Nanoboxx (under-the-seat subwoofer).
The stock system is now alive! I've had fairly expensive systems in the past (Infinity Kappa Components, JL Audio Amps, etc.). The Focal plug-and-play kit holds its own; I can't believe the stock head unit is powering them. The clarity and precision of sound being produced by these things is simply amazing.
On a side note, the Nanoboxx solves any low end fill desires anyone over the age of 16 will have. I literally have to turn the bass knob to its lowest setting or its too loud - hard to believe something that small can produce that much base.
PDA in Littleton, Colorado did the install so I can't comment on difficulty or anything. I didn't want to have to deal with pulling panels off or wiring the subwoofer.