Need more range!
5 channel amp
10" sub w/hideaway enclosure
High powered headunit
Does anybody have suggestions to improve the sound?
A high powered head unit should make no difference as far as power if your running an aftermarket amp or any external amp for that matter because the power is supplied by the external amp at that point not the amp inside the head unit. In your case you would be using a 5-channel amp so that amp is what dictates power.
For a good sounding system that hits the frequencies you are refering to you need a quality set of components up front. I have some new bass enhanced CDT front components that were just released. They would do well for what you are talking about. For the rear you can do 2 things. One is to run a coaxial that would give you some rear fill. Second is to run a quality midbass driver that would hit the kick drum the kick drum type frequencies and bridge any gap in range. I like that because the midbass drivers from CDT have broad range and actually hit midrange frequencies as well so they are a great rear fill that does not bring the ear backward by having high notes coming from there.
What sub are you going to run in the back?
The thing you want to do right now with the equipment you have is use a nice set of components up front. Skip all the other speakers for now. Run the doors and the the Thunderform off the amp. This would be a good sound quality type setup and give you good range and depth.
I have really nice component sets starting around $100.00 shipped that will get you what your looking for and sound good with your current and future sub.

