Been out of the car audio for about 5 years now ready to get back into it well to start what's a good 4ch amp for my 6.5 focals k5 would like nice crystal clear sound .
Depends on your budget. Some of the higher-end amps are Mosconi Zero 4 or Zapco Z150 LX... There are others. A couple of decent "bang-for-the-buck" amps are the NVX JAD800.4 or Zapco ST-4X II. Again, there are others.