New to audio...could use help

[bsauceda]

Hey im kinda new to the high tech audio, but Ive decided to upgrade.
I don't think im getting the full potential of my stuff and im looking to upgrade.
Heres what I have (its not the best) : Sanyo 720p 32'' , PS3 , Tivo HD w/ additonl external hdd , and a phillips HTS3544 surround sound. I dont care for it becuse the speakers plug in as clips. I think you can strip the wiring so they will plug into a normal reciever.

Also I have a 15'' sub in my car that I dont use, It has an amp but the power comes from a battery so im not sure if it will work inside. Is it possible to use this becuase it sounds great in my car??

Im using HDMI cords and a digital coaxil for sound from tv to reciever.
I want to get a decent reciever (around $300 or soo) then upgrade from their. Any suggestions on how to go about this.

Thanks Alot!
Brandon