Yes there is a big difference.
This is what marty always says:
That 1600W - they generally try and attract you with big numbers. Its probably not pure power and the ratings are most likley different (on those cheap amps)
Have a read of this - it might help
Reference: http://www.fhrxstudios.com/
So you have the hertz HSK 165s?
Man get a decent amp for those spilts and you will see a huge difference!! Trust me!!
Also before getting a amp/sub, i would sound deadned your doors!!
That alone will see BIG BIG difference!!
Since you have some quality gear, get a quality sub/amp
I would suggest the SR3 - 3 channel amp
1 channel for the sub, the the other for your fronts!!
DOOOOO IT