RF power amps require tuning but you seem to be indicating audio amps. As for using those lousyl STK and LM/TDA audio chips, don't fret over "tuning" them for high quality audio. While they may have decent specifications, they aren't much of a match against using vacuum tubes and discrete semiconductors as "the choice" for quality audio amps.
There are special pick-up microphones used in conjunction with a laptop and software to generate a response curve, but often that's for speaker setup and room acoustics, not so much the amp. There are methods to calculate and design low distortion, hi fidelity amps, starting with class type, stage coupling, preferred capacitor types in key locations, shielding techniques, etc.
Using a "radio" input as you mention (i gather you are using a broadcast radio signal) is far from providing a good source for measurements and adjustment. Build yourself a white noise generator instead, or build an audio sweep generator from one of many simple kits cheaply available on the Internet. You'll have low & high freqs. and everything in between to better test an amplifier's response, if that's what you're trying to do. Using your ears in place of an oscilloscope is only as good as the speakers you are listening to! Speakers and room acoustics can be deceptive but a calibrated scope doesn't lie. You can save some money and bench space by using your computer to generate audio sweeps (plenty of applets found on the Internet that do it for free) and you can buy Winscope software to have your 'puter become a scope.
Now go get yourself some 12AX7 and KT88 tubes or some Motorola power mosfets and make yourself a real good amp!