2002 Ford Focus Sony CDX-GT410u Sony XT-100HD HD Tuner Stock speakers, no amp, no subs
Yeah, since its been pretty well discussed in other threads we might as well roll with it. If its not going to adversely affect the head unit, I really doubt its going to affect an after market amplifier. Just make sure you take into account the increase in rms wattage its going to be feeding those 4x6's, don't want to over power them.
Pzaul