09 Yukon Factory (non-Bose) Stereo System

[yuk0n09]

I'm looking to replace all four (4) door speakers and the two (2) tweeters up near the windshield. I purchased this car last week (traded my 07 suburban LT with Bose) and have realized the sound just blows. In that regard, I have a few questions:

(1) What kind of wattage does the factory amplifier (if there is one) have?

(2) Are Polk Audio DB speakers a good choice?

Thanks in advance.