I can say that when I had my first inexpensive home theater in a box kit, an old Kenwood system, I thought that the system sounded quite nice. Then I went out and got some Definitive Technology speakers to replace the ones which came with the kit.
The jump in audio output and audio quality was unbelievable. Literally made a night and day difference to both audio quality and the volume I was getting from my cheap receiver.
If you are using the speakers which came with the kit, I think you will be blown away at the jump in quality you are likely to hear.
One thing to keep in mind is that I bought speakers that I believed I would be happy with for 10+ years of ownership. This is something I recommend to others. Don't buy one stop-gap product after another. If you are unsure, then you will want to make sure that there is a good return policy on whatever you buy so you can try them out, then return them if you aren't completely happy.
But, in my case, I was pretty darn happy.