Hmmm, the Lexus thing must have been discussed at a national dealers meeting, eh? The guy who told me that works in the Chicago suburbs.
If you are speaking of power amps to boost the L/R fronts, or maybe even the center, too.....I use a pair of IRD MB-100 monoblocks and recommend them without hesitation.
Check the various reviews that have been published on the MB-100's or the original nOrh LeAmp (the same thing).....they pretty much all agree that it is at least a good, if not outstanding, value. Used pairs are generally available on A'gon for $350 to $400, but might be a bit scarce. A pair shows up every month or so, I think.
Monoblocks would provide some flexibility for the future if you decide to go with L/R only now and add the center later.
The Parasound HCA-1201's are another bargain right now--but like the MB-100's, you can't find them everyday. The Parasounds probably have a higher current capability than the IRD's and have both balanced and unbalanced inputs.
Alternatively, another great value IMHO in power amps are used Acurus units. You might find an A200x3 to cover the L/C/R duty for $500-ish and the build quality would probably amaze you. The three channel versions are often available for not much more than the standard stereo models. As of last year, Klipsch could still supply spare switches and other unique parts for them (Acurus being the Toyota to Aragon's Lexus, Aragon now owned by Klipsch, you see
!)
Before the IRD's, I used an Acurus A150 for the front channels. Sold it a year later for just what I paid for it, too. (I had forgotten about that intermediate step in my first reply--the MB-100's were not the first upgrade, but done later when I was sure the system would be used way more for music than HT.)
I don't value putting more oomph in the surrounds, as once the load is taken off the front channels, my Onkyo is fine driving the center and rears in a 5.1 setup.