A amp always makes a difference.It will be a much cleaner sound and will also play much louder.
I had these speakers in my truck once and I had 50 watts going to them.They sounded pretty good.Polks dont really like a ton of pwer.I would keep it less than 100 watts rms.
Run those in the GF's car, first off HU power and now off a Profile amp. WAY better once amped. Speakers have a nice sound and get surprisingly loud...