But yet, none of them use Radio Shack Optimus amplifiers.

They don't have any amps that have the feature set I want. My amp-buying
strategy was to buy the cheapest possible amp that has the features I
needed. I was after multichannel amplifiers that took up little space and
had the internal crossovers necessary to triamp my front component set and
biamp my rears. Hence, I ended up with used older amps off of ebay. I have
18 channels of amplification in my car, and spent $400 in total.