ICE upgrade for my Indica turbo

Hi, I am planning for an ICE upgrade. I am not so good with brand stuff.

My current set up is

  • Blaupunkt Maui MP36 head unit
  • Two front speakers (on the end of the dash board, circular type I don’t know whats the real names of those kind of speakersstupid:)
  • Two oval speakers on the parcel tray.

Both the speakers are from GT series of Blaupunkt.

I am happy with the volume, quality, playback etc. from the current setup. The thing it lacks is bass. So I would like to add a sub and an amp to my current system. I am not an audiophile (hope the word is correct!!), and the budget will be alap (for me AS LOW AS POSSIBLE). In future (may be this year) I may go for another hatch, and I am looking forward to carry the sub and amp on to that. Is it possible?

In short my requirements:

  1. Good bass
  2. Sub + amp + necessary accessories
  3. Low budget
  4. Some what future proof ( for the carry over)

I hope my current speakers will sound fine with the add on sub.

So please suggest a good configuration Gurus, comments and suggestions are always welcome:)