I am looking to add lowers with built in speakers to my 2007 EGC. The dash speakers say "Hogtunes" on the back so I think they have been upgraded, but here's not much bass at all.
What is needed to add extra speakers to the standard radio?

 

You will definitely need a 4 channel amp, and if your adding lowers with speakers, I would upgrade the hogtunes speakers in your fairing.
A good starting point, budget minded, and just my opinion, would be a Stinger 700 watt 4 channel amp, mmat 601cx coaxial speakers in your fairing and prv 6.5" neo PA style speakers in your lowers

This will give you loud clear distinct tunes goin down the road.

OK Let the bashing begin.

 

Haha no bashing, I'll agree w you on amp and prvs but in my opinion if putting the prvs in lowers he should just go all pa style and get horns but then need a dsp. Ive not heard the mmats everyone praises but the simplest thing to me is run 4 of those and the stinger.