I have a Challenger 230 SE w/ Tower... I'm about to do my 3rd upgrade, although this is a fairly minor upgrade to the sound system. I live in Texas and many people at the lake beaches we hang out at have significant upgraded systems in their boats that drown you out unless you can provide significant sound output. My family and friends gave me a bit of a hard time because I'm an Audio/Video nut and knew I have gotten a killer deal on the boat.. all that being said if your budget is robust you can transform the system on the boat into audio heaven..
Pair of WetSounds PRO 485 Speakers on the Tower
10" JL Audio Subwoofer.. installed in the mid left passenger side area ( I'm either installing a second sub or upgrading to a 12" tomorrow ).. had a boston acoustics 10"
2 Alpine Digital Amps ( one 5 channel and one 4 channel ), non-marine installed in glove compartment.. no need for the marine versions as there is literally nothing different other than color and a higher price
Dedicated Marine Battery Bank ( 3 batteries )for Amp's and Stereo + Dedicated AC Charging System
Clarion IPOD Controller installer + Aux input module
Analog volume knobs for subwoofer and tower speakers
Kept stock clarion speakers, but I'm upgrading them to Alpine 7" speakers tomorrow